What Causes Vaginal Bleeding And Clotting Continuously?

I am 28 years old and have been bleeding for 11 straight days. After 7 days I went to the ER because fist size blood clots began to pass. My results did not show cist or pregnancy. The doctor also said my bloodwork was fine and to follow up with an obgyn. I have not been able to see one due to the holiday weekend closures. I am deeply concerned. I also have a 10 month old whom I'm nursing. Should I stop nursing? Why am I still bleeding? Should I go back to the ER? Please help!