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Ah, periods. They come, they go, they generally flow. But what happens when your period goes all “flow, interrupted” — starting, stopping midcycle, and then starting again?

Don’t panic. There are many regular reasons for an irregular period.

Before we dive into what’s not regular, let’s cover the basics of what is.

Your period by the numbers

Though it may feel much longer, the average period lasts only 2 to 7 days. During this time, women lose 2 to 3 tablespoons (or 30 to 44 milliliters) of blood. Some research shows that this number may be higher — up to 4 tablespoons (or 60 mL).

But more than just blood is expelled during your period. According to a small 1985 study, blood makes up only about 36 percent of your Shark Week output. The other 64 percent consists of tissue, blood clots, mucus, and uterine lining… but we’ll get to that in a moment.

Just as every woman is unique, so is her period, and it’s a-OK if the above stats don’t represent your normal.

In fact, for many women, an abnormal period is normal. According to the National Institutes of Health, 14 to 25 percent of women experience irregular cycles.

The following may be signs of an irregular menstrual cycle:

  • a longer or shorter period than usual
  • a lighter or heavier flow than usual
  • worse-than-usual cramps
  • “spotting,” or light bleeding between periods
  • other fun period probs

A typical menstrual cycle can be anywhere from 24 to 38 days long. During this time, the lining of your uterus — aka the endometrium — grows thicker and thicker as it prepares to take in and nourish a fertilized egg.

When there isn’t a fertilized egg to house, your uterus sheds the built-up tissue and blood. This lovely menstrual mixture makes its way through your cervix and out of your body via your vagina.

Fun fact:

The endometrial lining sheds at its own pace, which is why some days of your period are lighter and others heavier.

If the tissue trying to exit your body blocks your cervix, your period can temporarily stop or lessen. Once the blockage passes, it’s business as usual and your period will start back up.

This is just one cause of a menstrual pause. Other factors affecting your cycle can include:

  • stress (dun dun dun!)
  • sudden weight fluctuations
  • poor nutrition
  • illness
  • certain medications
  • hormonal birth control
  • too much exercise

Hormones play a big part in the literal ebb and flow of your period.

Levels of the hormones estrogen and progesterone become low at the start of your period, triggering the endometrium to start shedding.

Then your pituitary gland starts to amp up its production of follicle-stimulating hormone (FSH), which kicks your ovaries into estrogen-making mode. This generally happens in the first 4 to 5 days of your period.

Around the fifth or seventh day of your period, estrogen levels peak and your pituitary gland unleashes a wave of luteinizing hormone (LH). Progesterone levels also start to rise during this time.

Thanks to these changing hormone levels, a start/stop/restart of your period is likely to happen from time to time.

Some medical conditions can also cramp your menstrual style (get it?!). Hormones can be thrown out of whack by the likes of endometriosis, polycystic ovary syndrome, and fibroids.

Endometriosis

Endometriosis is a chronic condition in which the endometrial tissue that should grow inside your uterus grows outside of it instead.

This condition may be caused by:

  • menstrual tissue making its way to other areas of your body
  • high levels of estrogen
  • disruptions to your immune system
  • genetics

Endometriosis can cause painful periods and a bevy of other symptoms, including:

  • pain in your lower back, stomach, or pelvic region
  • pain during urination or bowel movements while menstruating
  • spotting between periods
  • pain during sex
  • infertility

Endo symptoms can often be lessened with over-the-counter meds like ibuprofen. Hormonal birth control or other hormonal medications are also an option. If your endometriosis is severe, surgery may be the answer.

PCOS

Polycystic ovary syndrome (PCOS) is a condition in which your ovaries produce higher-than-usual levels of the male hormones androgen and testosterone.

PCOS symptoms include:

  • irregular or missed periods
  • ovarian cysts
  • weight gain or difficulty losing weight
  • thinning hair or hair loss
  • acne on your face or body
  • skin tags in your neck and armpit areas
  • excess facial hair

The cause of PCOS is unknown, which makes finding a cure difficult. Thankfully, there are several ways to manage its symptoms and balance your hormone levels, including medications, changes in exercise and diet, and weight loss.

Fibroids

Fibroids are noncancerous growths that can develop in or on your uterus.

These growths can become large and painful in some cases, while in others there are no symptoms. That’s why, even though up to 80 percent of women experience fibroids by age 50, most of them don’t even know it.

When symptoms happen, they can include:

  • lower back pain
  • abdominal pain
  • constipation
  • longer or heavier periods
  • cramps
  • pain during sex

Fibroid pain can be eased with medication, dietary changes, holistic remedies (like yoga or acupuncture), meditation, or (in extreme cases) surgery.

If you experience any of the following during your period, it’s time to call your healthcare provider:

  • a period lasting less than 2 days or more than 8 days
  • heavy bleeding (one or more tampons/pads every hour for several hours)
  • severe cramping or other pain
  • periods that are less than 21 days or more than 35 days apart
  • weird vaginal discharge
  • symptoms of toxic shock syndrome (TSS), such as fever, diarrhea, or dizziness
  • sudden, irregular periods after generally having regular cycles
  • anxiety, depression, or other extreme symptoms of PMS
  • bleeding between periods or post-menopause
  • lack of a period for 3+ months when not pregnant
  • nausea, vomiting, or other extreme pain

In most cases, a stop-and-go flow is completely normal. Fluctuating hormones, stress, changes in diet or medication, and weight gain are just a few causes of an irregular menstrual cycle. Certain health conditions may also be the culprit.

Every woman is unique, and so is every period. What’s normal for you may not be the norm for someone else. You know your body best and can gauge when things seem a bit off.

If you start to have irregular-for-you periods on a regular basis, it’s time to talk to your healthcare provider. They can help you determine what’s disrupting your cycle and the best way to manage it.