6 weeks no heartbeat yet...should I be worried?

Shams
Hello everyone,
This will be my third baby (hopefully). I went for an ultrasound today and measured 6 weeks, however there was no heart beat or fetal pole. The technician said it's probably too early and I'll go back in 10 days for another. I also don't have any symptoms besides a little fatigue. I am trying not to worry but wondering if anyone has had a similar situation and everything worked out well. 
Thankyou!