5 weeks may be too early to locate a heartbeat. At this point you'll see just the sac where the baby is growing but not too much definition. I suggest you wait maybe 2 or 3 more weeks to repeat the scan for the heartbeat.
My doctor told me you wouldn't be able to hear the heart beat on the doppler until 12 weeks and your only 5 weeks so your barely pregnant i agree with the other girls it's most likey just to early wait untill 9 weeks and they should be able to see it on an ultrasound hope everything turns out to be ok for you and your baby good luck with it all
I wouldn't worry unless your hcg level drop as well. Good luck with everything! Try to stay positive and calm. I've been there so I know how you feel.
Sounds a bit early for a heartbeat. I wouldn't worry too much yet. Your hcg levels are normal.