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Periods are like snowflakes, no two are alike. Some women ride the crimson tide for just 2 days, while others experience a weeklong horror flick, and the range of blood (or uterine lining) shed is just as unique.

Pain is also highly individual; some women barely notice their period, while others resign themselves to the fetal position while cramps go all Mike Tyson on their nether regions.

After many a visit from Aunt Flow, you tend to know what to expect. As long as your periods feel mostly the same from month to month, you need not fret.

However, there are some symptoms that should raise a red flag, especially if they’re not part of your monthly routine. Here are the ones worth contacting your doctor about.

As we’ve already discussed, “normal” is a flexible term when it comes to describing periods. Most women have a cycle that lasts 21 to 35 days. However, if your periods come to a screeching halt, you may or may not have a baby on board.

Once you’ve cleared that question up with a simple pregnancy test, here are some other factors that could be to blame:

  • Stress. Believe it or not, being under stress (especially when its chronic) can throw a wrench in your menstrual activity.
  • Extreme fluctuations in weight and physical activity. Losing or gaining a lot of weight can affect hormones that keep your menstrual cycle in check, as does over-exercising. If you don’t have enough meat on your bones (specifically, body fat), your body won’t be able to manufacture its period-producing hormones.
  • Polycystic ovary syndrome, aka PCOS. Hormone imbalance is part and parcel of this condition, as are cysts on the ovaries.
  • Hormonal birth control. If your preferred method of birth control is hormone-based, it could affect how often you get your period, or stop it altogether.
  • Perimenopause. This is the timeframe leading up to menopause. If you’re at or beyond the upper limit of your 40s, your body may be flirting with menopause. If your periods have ceased fire for 12 consecutive months, consider the courtship consummated — you’re officially in menopause. However, your periods can be out of whack for a few years beforehand.

As a rule of thumb (or uterus), bleeding through one or more tampons or pads per hour is a sure sign of menorrhagia, which is a very difficult way to spell abnormally heavy menstrual bleeding. This condition isn’t just inconvenient. You may also display symptoms like shortness of breath and anemia.

Menorrhagia isn’t all that rare, and about 30 percent of women talk to a doctor about it at some point.

Here are some common culprits:

  • Cancer. DON’T FREAK OUT. We’re leading with the worst-case scenario. Uterine or cervical cancer can cause a heavier-than-normal flow, and these cancers are usually diagnosed post-menopause.
  • Bleeding disorders. Like Von Willebrand disease, an inherited condition that affects clotting. These disorders can also affect the heaviness of your flow.
  • Endometriosis. Having this condition means that the tissue that normally lines your uterus and sheds during your period has set up shop in other parts of your pelvis, like your ovaries or fallopian tubes.
  • Adenomyosis. Not unlike endometriosis, this means that the tissue that’s supposed to line your uterus has grown into the uterine wall.
  • Your IUD. Certain types of IUDs (intrauterine devices) come with a side (effect) of heavy bleeding, especially during the first year of use.
  • Fibroids or polyps. As scary as these words sound, they’re in fact noncancerous growths that can pop up in your uterus and can cause heavier than normal bleeding.
  • Hormonal imbalance. PCOS isn’t the only condition that can wreak havoc on your hormonal equilibrium. An underactive thyroid (hypothyroidism) can also be to blame. Certain hormonal shifts actually cause your uterine lining to thicken, and where there’s thick uterine lining, there are heavier periods.
  • Pregnancy complications. Miscarriages and ectopic pregnancies can cause especially heavy bleeding. It’s important to keep in mind these things can happen very early on, so you may not have even noticed you were pregnant.

A notably brief trip to period-town may not be cause for concern, especially if that’s just the way your body rolls. Remember, periods typically last 2 to 7 days, and every woman is a proverbial Goldilocks — there’s a period length that’s “just right” for her.

Keep in mind, menopause can cause disruptions in your cycle and hormonal birth control can speed it up. On the other hand, some of the things that may put you at risk for heavier bleeding have a tendency to cause longer bleeding as well.

If anything seems out of the ordinary, best to call your healthcare provider.

The truth hurts… literally. Cramps are simply part of the package deal when it comes to periods.

When your uterus is contracting to push out your uterine lining, a little discomfort is to be expected, and it usually starts 1 to 2 days before you start to bleed. Rest assured, your suffering will typically last only 2 to 4 days.

However, some less lucky ladies may have dysmenorrhea, or cramps that are much more severe than your run-of-the-mill, standard period stuff.

If you’re looking for something to blame for your vicious cramps, here’s where to start:

  • your IUD
  • fibroids
  • pelvic inflammatory disease (PID)
  • stress
  • endometriosis
  • adenomyosis
  • sexually transmitted infection (STI)

Light spotting or bleeding between periods isn’t always serious. Simple things like switching your birth control can leave their literal mark. However, other reasons may require medical attention.

Here’s a few more serious reasons you may be bleeding when you’re not supposed to:

  • perimenopause
  • pregnancy
  • miscarriage
  • ectopic pregnancy
  • cervical, ovarian, or uterine cancer
  • uterine polyps or fibroids
  • PCOS
  • STDs (hello, chlamydia and gonorrhea)
  • an injury to your vagina (which can happen during sex)

Like cramps, breast tenderness is pretty common during your period. The pain you experience in your wobbly bits is likely caused by changes in your hormone levels. The discomfort can extend as far north as your armpit, where there’s some breast tissue that goes by the excellent name “The Tail of Spence.”

If your breasts hurt outside your monthly cycle, get thee to a doctor ASAP just to be safe. In incredibly rare cases, breast pain can be a symptom of cancer.

What’s going on in your uterus can affect its neighbors. One study found as many as 73 percent of women have reported having diarrhea, abdominal pain, or both during that time of the month.

If this is part of the standard operating procedure of your period, it’s most likely nothing to worry about. If not, it could be a sign of another medical condition like PID. Excessive fluid loss through diarrhea can cause dehydration, and you should see a doctor if it gets out of hand.

Some clotting is normal during menstruation, especially on a heavier day. While your uterus is shedding all that thickened blood and tissue, your body comes to the rescue with anticoagulants to help thin things out and flow more smoothly. But it can’t always keep up with your flow, and that’s when clots happen.

Some more serious causes of clotting include:

  • endometriosis
  • adenomyosis
  • cancerous tumors
  • fibroids

If you’re suddenly experiencing clotting, or it happens more consistently, talk to your doc.

Once again, period blood and texture varies from woman to woman. However, pink and watery menstrual blood could be a sign of low estrogen levels in the blood.

Estrogen helps stabilize your uterine lining, so if you don’t have enough, you may spot in various hues (including pink) throughout your cycle. So keep an eye out.

Note that low estrogen levels can be caused by perimenopause or hormonal birth control that doesn’t contain estrogen.

Some other symptoms of low estrogen include:

  • lack of vaginal lubrication (which can cause painful sex)
  • fatigue
  • trouble concentrating
  • mood swings
  • depression
  • headaches or worsening of pre-existing migraines
  • hot flashes
  • breast tenderness
  • increase in urinary tract infections (UTIs) due to a thinning of the urethra