In need of advice! Pls read

So I went to the ER last night with heavy bleeding and some clotting. I am 12 w 5 d pregnant. My cervix was not dilated, baby had a heart beat of 154, and HCG was 78,000 (that said that was right where it should be), I also had an ultrasound that showed a very active and what seemed to be healthy baby.

They said they saw where I was bleeding, and it was on the opposite side of my placenta and that's a good sign. But they don't know why I'm bleeding??? Has anybody ever had this happen??? What was your outcome???

I cried like a baby when I got to see my little bean in there jumping and active. I don't want to lose this baby.