Threatened Miscarriage

Im currently 12weeks and 3 days. The cramping started around 1am and the bleeding followed shortly after that. It was a LOT of blood. I kept bleeding heavy at the hospital. She used her fingers to check my cervix and it was closed but more blood came when we she did that. I waited two hours and the ultrasound tech came and got me. She did and vaginal ultrasound and of course more blood filled the table. She started smiling and said she couldnt get a heartbeat because the baby kept MOVING an she showed me and then she found the heartbeat it was 160. What im worried about is i lost maybe 2 pints of blood between last night and this morning and they had no idea why i was bleeding and cramping or what caused it. I never found out ive already left the hospital im not bleeding now but im still concerned about why it happened. An i still have doubt about what the ultrasound tech said about the baby being completely okay...