miscarriage?! normal?! I need answers.

I'm 8 weeks today and yesterday after having sex had a fair amount of brown blood come out. Maybe half a pad- full pad. It stopped quick but I've been cramping last 2-3 days and the pain is getting worse but not really sure if it's even cramping. I went to ER last night and they did u/s saw a baby and heartbeat was 150. They said blood had came from cervix and cervix was closed. I'm still cramping though and it hurts. Any reason why?!?! Am I going to miscarry?! I've miscarried once and have 2 healthy children brought to term with no problems. Why the hell am I cramping?! Please just be straight with me about experiences. Spare any false hope. I just want facts and answers. TIA
***UPDATE***
Doctor said I have subchorionic hemorraghes which is normal and should go away but I had a healthy baby and the cramping is more than likely my muscles accommodating my baby.