When i was 5 wks i had an u/s done, due to miscarrying earlier. and there was nothing there. 3 wks later i had another one, and we say the little peanut and hte heartbeat
Do you know how late your period is? Or when your last period was? I think it just may be too early to see anything yet. Some women don't see anything until closer to 7 weeks.
You could be very early on in your pregnancy so naturally, they wouldn't be able to see anything. What were your levels? that can sometimes indicate how far along you are (but not always).