Every month my period is different. Sometimes it lasts a long time and is heavy; other times it's the opposite. My friends say that is not normal and I need to go to the doctor, but I have no idea what to do! What could be going on?
- Elia*

It's not unusual, especially in the first couple of years after you've begun menstruating, to have an irregular menstrual cycle or even miss a period. Many girls also notice changes in the flow and duration of their periods from month to month.

Though irregular periods are common, it's always a good idea to talk to your doctor or nurse practitioner about it if your periods last longer than 7 days, are very heavy, come more often than every 21 days, or had been regular and now suddenly are different.

Some medical problems (such as hormone imbalances or clotting disorders) and other things (such as stress or too much exercise) also can affect periods. Prolonged or heavy bleeding can lead to anemia — and you don't want that. An evaluation by a doctor can help determine the cause of any possible problems.

Reviewed by: Larissa Hirsch, MD
Date reviewed: July 2011

*Names have been changed to protect user privacy.