If you are 100% sure when your period started then it may be true.
It is so horrible to go through a miscarriage...I hope that its not the case for you, but if it is there are many women here that are ready to comfort you. I had a similar situation but baby was at 8.5 weeks, I was 11....I could also clearly see my baby on the screen..not moving...it was terrible. I got the D and C the next day.
I am confused as to why your doctor made you wait a week. Have you had any bleeding or anything?
If you got your period wrong by a few weeks, or if you are irregular and dont know exactly when you ovulated then the baby could be at 6 weeks with a heartbeat to small to be seen. It seems odd that you would have gone for four weeks without knowing anything was wrong. Anyways...in my case, it was a miscarriage...and now I am looking to trying again. But I dont know about you, just know that it does get easier as time goes on. The first week I would cry randomly and just felt like staying in bed for the rest of my life. But now almost three weeks later I feel better...and are waiting for the next baby.
Do you have children? How old are you? Whats your preg. story?
I hope it all works out.