Anyone else experience this

I am exactly 5weeks and 3days went to the hospital because I didn't feel pregnant so I felt something was wrong well I went and got my urine done blood test done and a ultrasound my urine was great my hcg level is 20k and the ultrasound sound was normal only thing was in Doctor's words "unable to see heartbeat" so I'm told to follow up with my obg to re due ultrasound in a few days to see if my baby shows a heartbeat should I be worried or has anyone else had a positive outcome?