Bleeding behind the placenta

Has anyone had this? I was cramping yesterday and decided to go to the er bc I was worried. Ultrasound showed baby heartbeat and moving but there was a little bleeding behind the placenta. I have an appt with my ob tomorrow and spoke to the on call doc at the office who didn't seem to worried and he sounded like this was kind of common . But he did say to relax and wait to see my ob tomorrow and no sex till after speaking with him. He also said it doesn't mean u can't miscarry but it's kind of common. Please tell me someone else had this and everything was fine. I'm so nervous right now. The cramping is more of pressure and pulling not really cramping. Thanks all for reading.