Sarah M. replies:

Bleeding for more than two weeks at a time is a good reason to see a doctor, at least to make sure you haven't become anemic (iron deficient) due to blood loss, and to rule out pregnancy as a cause of the bleeding if that is a possibility. It is most common for a period to last 4-6 days, but everyone is different and it is not necessarily a problem to bleed for longer. A doctor may recommend checking your hormone levels and the health of your endometrium, to make sure that the bleeding is not a symptom of an underlying condition or imbalance.

As for skipped periods and cycles of different lengths, it is very common for young people with periods to experience irregular menstrual bleeding. If you had your first period within the last five years or so, it is probably just a matter of staying healthy and waiting until your body settles into its cycles.

Irregular periods are also a normal occurrence after pregnancy and breastfeeding, after stopping hormonal birth control or hormone treatments, and in the years before menopause. Good nutrition, regular exercise and general health can make these transitions smoother, but it takes some time for the body to adjust to different cycling situations.

Other than big hormonal events like puberty or pregnancy, emotional and physical stress (poor diet, relationship conflicts, sudden weight changes, over-exercising) are common causes of irregular periods. Menstrual periods are a sort of vital sign that way-- they can signal when something in your life needs adjusting, but they aren't necessarily a problem of themselves.

If you want to understand your periods and cycles better, either for yourself or to have information to give a health provider, a great strategy is to keep a simple daily diary or chart about your cycle. There are lots of blank cycle charts online that you can download and print for free, or you can make your own. I like the menstrual cycle diary from the Centre for Menstrual Cycle and Ovulation Research.