TMi photo - 15 week bleed update and answers

I posted earlier this morning for prayers cause I was 15 weeks and gushing blood heavily. I went to the ER my urine was clean, the baby heart rate was 158 and moving all over the place, and the placenta looked good and baby was measuring 16 weeks 2 days.... But they are not sure what was causing me to bleed. 5 hours of bleeding it's died down and turning to brownish. I'm still so worried and terrified I will lose this baby has anyone experienced this???