What Causes Heavy Vaginal Bleeding With Clots?

Hi, may I answer your health queries right nw Please type your querhy here... This month I missed my period. I took 2 tests but both shoes negative. I had symtoms of pregnancy. A week after taking the tests my symtoms stopped and I startin bleeding heavy and passing clots I had abdomal pain and my back was also sore. The bleedin reduced after 3 days I have no been bleeding for 6 days now. I'm seeing my doctor on Friday but I need an some sort of answer now