Is it normal for having period for more than 3 weeks?

No.: Prolonged menstrual periods usually indicate a hormonal imbalance. If the lining of the uterus isn't shed completely each month, it can build up and cause a prolonged period. The source of the imbalance can be the ovaries, the thyroid gland or the pituitary gland. Prolonged and/or heavy menstrual bleeding can lead to iron deficiency anemia. Please get it checked out. Dr. Anne.

No. See your Doctor: Menstruation usually lasts 5 days. Abnormal or prolonged vaginal bleeding can be due to diseases of the reproductive tract(such as uterine fibroids, cervical polyps, cervicitis, cancer), bleeding disorders, dysfunctional bleeding from hormonal causes including anovulation which can be due to emotional or physical stress, obesity, anorexia see> http://bit.ly/19cKee5 and http://bit.ly/1Cn3tey