What could possibly be wrong with me?

Hi! So I have been having a little problem. My periods gave been lasting about 2-3 weeks. My doctor put me on a hormone for a few days to make it stop and did some test, all the tests for pcos (or whatever it is) came back negative. Ever since I stopped the hormone as instructed by the doctor I have been bleeding, it's been about 8 days and it hasn't stopped. Does anyone have any idea what could be happening? I am trying to get pregnant, but I am unsure if I can at this point.