Had the same story with my pregnancy... Wait for 2 weeks and go for another ultrasound. In the meanwhile do blood test for BHCG two days apart. The second test should show that your numbers doubled - which confirms you are pregnant. That's what I did. I was about 5 weeks and they saw nothing on abdominal u/s. We did blood work it came 1945 units. The doc told me to wait for two weeks and do a home pregnancy test suspecting that it is either an early miscarriage or a blight ovum. I couldn't wait for two weeks going nothing and thinking of miscarriage so I went for another blood test 2-3 days later, and my results were 4470 units. Which proved that I was pregnant and it's not a miscarriage. Because in miscarriage the hormone level would drop and in pregnancy it doubles every 36-48 hours at this stage in pregnancy. So about a week and a half after that last test I went for an u/s and saw a heart beat which confirmed I was 7 and a half weeks pregnant. Don't worry, take action, and good luck.
Don't be. It's really too early. All you would see now is the sac. I was actually @ 6 weeks, 3 days & we saw nothing. I went back in 2 weeks & saw my baby's fluttering heartbeat.