Hi, I've had my period for 13 days now and it is very light but it will not stop! I've had this problem a year ago and that time it stopped around 21 days after the period started. This time I'm kind of scared because I've started running long distance and my friends say that may have something to do with it. Should I go see a doctor?

Yes, excessive exercising can lead to irregular periods. It would be best for you to see a doctor and get all of this straightened out.

Prolonged bleeding should always be discussed with a doctor to make sure there isn't another underlying problem. See your doctor! :)