Had a scare!

I am 12 weeks and 5 days pregnant, 2 days ago I started bleeding heavily and went to the ER. After tons of blood work, urine tests, and an ultrasound we found out that our baby is completely healthy. Our baby was moving like crazy and the heartbeat was very strong! I'm so happy that the baby is doing amazing but it still worries me that they have no idea why I'm bleeding. Which now it's just drops of blood every little while, still scary though. But doc said everything looks normal and not to worry. Anyone else have this issue??