Trying to stay positive

Tracy
I went in for my first u/s today and we were only able to see the gestational sac and yolk but no heartbeat.  I was so disheartened and I'm praying everything is ok.  I'm also praying I got my calculations wrong and it's just too early to see anything.
I had my regular period in July and that would make me 7 weeks/6 days.  2 weeks after my regular period, I had another period in August.  It was heavier than my normal but didn't last as long.  The second period would make me 5 weeks.  
Has this happened to anyone?  My doc is having me come in next week to see if we can see a heartbeat.