6 weeks, I am worried

Ashlie
I had an ultrasound, I am 6 weeks pregnant.... and they could only see the yolk sac, and was not able to see a heartbeat. .. this is my four pregnancy... with my other I didn't even know I was pregnant until 12,14 and 16 weeks... so this is new to me... doctors told me this normal, not to worry... usually don't see a heartbeat until 8 weeks...