Got two X chromosomes? Then you probably know your period can be more like your flaky friend who always shows up late to drinks (and sometimes not at all) than that super-organized friend who’s early to every group dinner.

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First of all, don’t freak out. Irregularities in menstrual cycles aren’t all that rare. Many women experience a missed period every once in a while, and three to four percent of all women will skip at least three cycles at some point in their lives (a condition technically known as oligomennorrhea).

While your initial—and very valid—reaction to skipping a cycle might be that you’re pregnant, a number of lifestyle and health factors can also prompt our menses to take a mini-vacay. (Still, never wait to take an OTC pregnancy test or visit your doc for a blood or urine test to rule out a potential pregnancy.)

But if you’ve skipped three or more periods, and you’re sure you aren’t pregnant, paying a visit to your OB/GYN, GP, or an endocrinologist is non-negotiable. In the meantime, here are seven common reasons your periods could be AWOL—and what you can do to get things back on track.

1. You’re stressed.

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From feeling like we have no control over our job to being abused or living in an unsafe environment, chronic stress takes a serious bite out of our bodies’ well-being. Too many stress hormones coursing through our bloodstreams signal our brains to slow down or temporarily stop ovulation until our environments become safer for bringing a new baby into the world.

2. Your diet is sub-par.

What and how much you eat play a big role in how regular your cycle is. Not noshing on enough healthy food deprives the body of key nutrients like calcium, magnesium, iron, and zinc—all of which are required to make sex hormones (among other internal upkeep).Dietary recommendations and athletic menstrual dysfunction. Manore MM. Sports medicine (Auckland, N.Z.), 2003, Mar.;32(14):0112-1642.Low nutrient and calorie availability strikes our systems as another form of stress, especially if we lose too much body fat as a result, sending our ovaries the message it’s definitely not the time for fertility.Meal times are important as well: Numerous studies confirm that young women who skip breakfast have more menstrual irregularities than those who pencil in the most important meal of the day.Skipping breakfast is associated with reproductive dysfunction in post-adolescent female college students. Fujiwara T, Nakata R. Appetite, 2010, Aug.;55(3):1095-8304.

3. You exercise a lot.

Menstrual irregularities are surprisingly common among physically active women. About one-third of female athletes (amateur or pro) either don’t get a regular period or they’ve recently skipped three or more cycles in a row.High prevalence of subtle and severe menstrual disturbances in exercising women: confirmation using daily hormone measures. De Souza MJ, Toombs RJ, Scheid JL. Human reproduction (Oxford, England), 2009, Nov.;25(2):1460-2350.Properly refueling our bodies to keep pace with how much we exert ourselves isn’t always easy (especially when social pressures cause some of us to shy away from packing away heftier meals).Consumption stereotypes and impression management: how you are what you eat. Vartanian LR, Herman CP, Polivy J. Appetite, 2006, Dec.;48(3):0195-6663. But the greater the imbalance between how many calories we incinerate and how many we swallow, the trickier the timing with our cycles. Even if we’re able to eat enough to offset unnecessary weight loss, research shows exercise lowers the amount of female sex hormones (namely: estrogen and progesterone) swimming around in our systems. When we go overboard on exercise, and these hormones dip too low, we dampen part of the chemical communication chain that normally gives rise to predictable periods.And remember, this isn’t a side effect to ignore. Some women with amenorrhea related to eating disorders or excessive exercise can also be predisposed to heart disease, osteopenia, and osteoporosis later in life, Tyson says.

4. Your weight is too low (or too high).

Being underweight can stop Aunt Flo in her tracks. In part, because less fat means lower levels of leptin—a hormone produced by fat cells that plays a huge role in triggering ovulation and menstruation, says Sherry Ross, M.D., an OB/GYN and women’s health expert at Providence Saint John’s Health Center in Santa Monica, CA.Too much body fat can also disrupt coordination between brain and ovaries: Between eight and 18 percent of obese women in several studies report irregular cycles. Sometimes this means shorter or heavier periods, or a shutdown of a few cycles altogether.There’s no specific weight above or below which you’re guaranteed to stop ovulating or menstruating, says Nichole Tyson, M.D., an OB/GYN at Kaiser Permanente and member of the American College of Obstetricians and Gynecologists. “Everyone has their own set point,” she says. So don’t stop seeking answers for why your cycle’s out of whack simply because you’re a few pounds heavier or lighter than your friends. (In other words, keep reading.)

5. You have hormonal issues.

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Having an under- or overactive thyroid can also give rise to unreliable menses, says Dena Harris, M.D., OB/GYN, and founder of SoHo OB/GYN in New York City. According to the American Thyroid Association, approximately 20 million Americans have some kind of thyroid disease—with women being five to eight times more likely than men to be diagnosed. Hyperthyroidism is characterized by heart palpitations, weight loss, intolerance of heat, and increases in appetite, sweating, and bowel movements. Hypothyroidism symptoms include weight gain, lethargy, depressed mood, facial puffiness, constipation, and a slower heart rate.A condition called polycystic ovary syndrome (PCOS) may also be a cause for missed or irregular periods, Tyson says. In PCOS, there are imbalances in estrogen, progesterone, and androgen (a male hormone women usually produce in far smaller amounts), which can lead to irregular or infrequent ovulation.PCOS affects between one in 10 to one in 20 women—or about five million women in the U.S., according to estimates. Symptoms vary but can include acne; thinning hair; increased hair on the face, back, or chest; obesity; and type 2 diabetes, explains Jaime Arruda, M.D., an OB/GYN at the University of Colorado, Hospital.Finally, premature ovarian failure (or POF—a.k.a. early menopause) may also explain why a younger woman’s periods may be absent for many months.One thing to keep in mind: If you have female relatives also experience missed periods, this may be the initial and sometimes the only flag that you may have thyroid disease, PCOS, or POF, because these tend to run in families. If any of these above signs ring a bell, see your doc ASAP. “Women with PCOS can have long-term risks of serious health conditions, such as heart disease and diabetes,” Tyson says.

6. You’re taking certain meds.

Some OTC painkillers—like aspirin, ibuprofen, and naproxen—have been found to screw with our menstrual cycles, Ross says. As can some thyroid medications, since they alter the levels of hormones that interact with initiating ovulation and menstruation.Certain antidepressants like Prozac and Zoloft can increase our body’s levels of prolactin—a hormone that normally promotes lactation following pregnancy but also shuts down our menstrual cycle, Harris adds. Opioids (prescription pain meds), blood pressure medications, and antipsychotics can also affect menstrual cycles, according to Arruda.

7. You’re on birth control.

Most birth control pills and patches prevent pregnancy by halting ovulation. Sometimes this also results in a few periods being skipped as well. This is totally normal in many cases—and, Ross says, often welcome by women who prefer a lighter or less-existent cycle.But if you go off the pill and don’t resume menstruation within three months, something else may be going on in your body. From weight, diet, or exercise-induced absence of menstruation to some other hormonal issue at play, Ross says the pill can mask underlying issues that only surface once the regimen’s stopped. (IUDs, on the other hand, do not halt ovulation, Ross notes: “You still ovulate, but IUDs create an inflammatory reaction in the uterus that prevents sperm from accessing the fallopian tube, where fertilization would take place.” Curious? Here’s how to decide if an IUD is right for you.)

Your Action Plan

Most of the above issues can be tested for, and while some can’t be completely resolved, hormone-replacement therapies and lifestyle changes (think: cutting back on common stressors or trying meditation and other ways to relax) can help re-regulate your cycle and address other imbalances, Harris says.

There are also hormonal options, such as birth control pills or progesterone, or acupressure or homeopathic alternatives that can regulate and balance out your periods, Ross says.

If over-exercise, caloric restriction, or low body-fat percentage is the cause of missed menses, hormone-replacement therapies or birth control are often the go-to Rx, Tyson says. But she cautions against opting for this without addressing the underlying eating disorder or unhealthy relationship with exercise.

The supplement aisle can also be helpful. Research shows calcium, zinc, iron, and vitamin D can be beneficial to compensate for these minerals’ lower abundance in cases of dietary restraint or exercise-induced loss of periods. In addition, adding around 360 calories of protein and carbs on days women exercise can help bring their menstrual cycles back.Dietary intervention restored menses in female athletes with exercise-associated menstrual dysfunction with limited impact on bone and muscle health. Cialdella-Kam L, Guebels CP, Maddalozzo GF. Nutrients, 2014, Jul.;6(8):2072-6643.”>Dietary intervention restored menses in female athletes with exercise-associated menstrual dysfunction with limited impact on bone and muscle health. Cialdella-Kam L, Guebels CP, Maddalozzo GF. Nutrients, 2014, Jul.;6(8):2072-6643. The precise amount will vary, depending on your body, which is why a dietician or nutritionist—preferably one who specializes in eating disorders or sports nutrition—can offer some help.

The bottom line? If you miss more than one period, you’re sure you’re not pregnant, and you’ve exhausted all possibilities, it may be time to make some lifestyle changes. Talk with a healthcare provider about hormonal and other medical issues that could be getting in the way of your flow.