no sac

I went for my first ultrasound at 5 1/2 weeks last Friday (I know that's really soon) but the girl that scheduled me was new and didn't know I should have been scheduled until I was at least 8 weeks , anyways the dr did an ultrasound sound  and it said she would be looking for atleast a sac but no baby since it would be too soon. When she did the ultrasound (vaginal) THERE WAS NO SAC! It freaked me out , I'm trying not to stress , she wanted to check my hcg levels to make sure it wasn't an ectopic pregnancy , my levels came back 1065, she told me it was normal and to re take the lab work Sunday (which I did) in hope that's my hcg levels doubled. She is to give me the results Tuesday , has this happen to any of you ladies? I just turned 6 weeks today. I don't really feel any symptoms besides gas and fatigue. This is my first pregnancy too btw...