I Have Been Having Vaginal Bleeding Now For About 8

I have been having vaginal bleeding now for about 8 days. I was cramping about the first couple of day and now I'm not. I am not having any pain, just the bleeding. Why am I still bleeding? I started bleeding a week before my period and I am still bleeding during the time of my period. I took pregnancy tests and all are negative. I am only 21 years old and don't have any children.