7.5 weeks..what should I expect at ultrasound today?

I had one at 5.5 weeks and they saw nothing. I am kind of worried today because I have read that by now they should be able to see the heartbeat. anyone else had this happen?? I don't have many symptoms...only sore bbs and nausea(for 2 days only)...so that also worries me! thank uin advance=)