Going out of my mind

It is first time for me to be pregnant...
Doctors beleive that i should be 9 weeks pregnant, but the ultrasound shows that i am 6 and 1\2 weeks pregnant... according to the calculatins on the internet i should be 8 weeks pregnant...
The doctors can not make up their minds whether there is heart reaction or not. One is waiting for a sound, but my dilema is: "are the speakers on?!?" The other one sees something blinking on the monitor, but my dilema is "is it the heart reaction?!?"
The only thing they suggest is me having a rest and another examination in a week or two.
I think i am going out of my mind. What the hell is wrong and who is wrong?
I know when i got pregnant, but how can i know for sure how many weeks i am pregnant and how can i know that there is a fetus and that it has heart reaction?
Am i exaggerating?