Plenty of women who get their periods are well acquainted with monthly cramps, cravings, mood swings, and fatigue. But there’s a real difference between annoying symptoms that are par for the course and others that are actually cause for medical concern.

We asked experts to weigh in on period symptoms that may serve as red flags. If you experience any of the six following symptoms, you’ll do well to schedule an appointment with your healthcare provider.

1. Excessive bleeding (also known as menorrhagia)

Although you may feel like your periods are heavy, needing to change a pad or tampon on the hour every hour is not normal, warns Sheeva Talebian, MD, co-founder of Truly MD (an informative blog about health written by doctors) and director of third-party reproduction at the Colorado Center for Reproductive Medicine in New York City.

Related: Shop products to help get you through your cycle.

Bleeding heavily could indicate an “anatomic problem, like fibroids (noncancerous tumors of the uterus) or polyps (small, benign growths on the lining of the uterus), or it could be a miscarriage,” she notes. It could also be a result of a hormone imbalance or adenomyosis (a condition in which glands from the endometrium become embedded in the uterine muscle), or a complication related to medications or other medical conditions.

Dr. Talebian suggest seeing your doctor ASAP if the heavy bleeding continues, especially for several days.

2. A particularly long period (also known as metrorrhagia)

Some women bleed for four days, some for a week. But if your period lasts longer than seven days, you should see your doctor, Dr. Talebian says. As with menorrhagia, bleeding for this long may be an indicator of an anatomic issue or miscarriage.

3. Large clots

Generally, clots—a coagulation of the thick lining in the uterus—are considered normal. This is because your body releases anticoagulants during your period, but sometimes the flow of your period is too quick for the blood to de-clot.

However, if you happen to pass a blood clot that is bigger than a silver half dollar, check in with your doctor, says Jenepher K. Piper, MSN, CRNP, a Certified Registered Nurse Practitioner specializing in Family Medicine at Hunt Valley Family Health, an affiliate of Mercy Personal Physicians in Lutherville, Maryland. “This could be a sign of fibroids or a bleeding disorder,” Piper notes.

One such bleeding disorder is Von Willebrand’s disease, which prevents blood from clotting properly.

4. Intermittent bleeding throughout the cycle

Spotting, especially out of the blue, could be cause for concern, Piper notes. According to the US National Library of Medicine, vaginal bleeding that occurs between periods is typically benign and treatable. However, there are cases when the bleeding may indicate a greater health concern. So, if you’re spotting (especially if that spotting is heavy), you’ll want to see a doctor.

5. Periods that are extremely light

It may sound like a dream to some women, but a light period isn’t always a good thing. “[A very light period] could indicate a lack of ovulation or damage to the uterine lining,” Dr. Talebian explains.

Light periods may also be a sign of an ectopic pregnancy, especially if accompanied by sudden fainting, abdominal pain, and shoulder pain, according to the Mayo Clinic. An ectopic pregnancy occurs when a fertilized egg implants somewhere other than the uterus. They can be very harmful, so see a doctor immediately if this is a possibility.

6. A sudden fever, vomiting or diarrhea, a rash resembling a sunburn, or feeling sick after using tampons

If you’ve been using tampons and are suddenly feeling like you’ve come down with a weird bug, check in with your doctor.

Symptoms may be linked to toxic shock syndrome (TSS), a rare, life-threatening complication of certain types of bacterial infections, such as Staphylococcus aureus (staph) bacteria or group A streptococcus (strep) bacteria. Toxic shock syndrome has been associated primarily with long-term use of superabsorbent tampons. Thankfully, the tampons connected to TSS have decreased in the marketplace, and in turn, incidence of the condition is on the decline.

Related: An All-Natural Guide To Surviving Your Period With A Smile

The Bottom Line

According to the Mayo Clinic, women should also take any of the following patterns or symptoms seriously:

• Your periods suddenly stop for more than 90 days—and you’re not pregnant.
• Your periods become erratic after having been regular.
• Your periods are less than 21 days or more than 35 days apart.
• You develop severe, debilitating pain during your period.

There are plenty of possible culprits—from lifestyle factors (like how much exercise you get) to diseases, fibroids, and birth control—that could lead to abnormal menstrual symptoms. They generally can’t be diagnosed without a medical professional, so it’s wise to take note of what you’re experiencing, and when and how often, and then talk to your doctor.