Negative blood types

Has anyone else been the momma with a negative blood type and daddy have a positive? I had an ultrasound today at 7wks 4 days to figure out why I'm bleeding and they found a very strong heartbeat along with a perfect baby but I have a lot of free flowing blood next to the sac.. They think it may be my body trying to fight the pregnancy if the baby is positive. They just gave me a shot to help protect the baby I just want to know other mommas stories!!