extremely worried

I had a miscarriage back in Oct 2014 and I've been ttc ever since. I found out I was pregnant in March. I've had one ultrasound and I've heard my baby's heartbeat twice. The first time it was at 150 and the second it was at 138. I have an anterior placenta and I haven't felt baby move. I am currently 18 weeks today. I have the anatomy ultrasound on July 10 but I am worried there won't be a heartbeat or something will be wrong.