I'm 19. Last month I had my period for 17 days, which is very abnormal for me. I was also dizzy and had bad headaches. I finally got into a doctor since I was really scared something was very wrong. The doctor did an ultrascan and found a 1" cyst on my ovary. It was a harmless cyst, but she said that since it was on my ovary, that was causing changes in my hormones, causing my period to last longer. After my period ended, it started up again a week later. A week later I was experiencing sharp pain by my hip for three days straight, so I got into the doctor again. The cyst had popped, which was a good thing, since it's gone now. So far my period's been normal again. I would suggest just going into a doctor and making sure everything is okay.