Worried and nervous

Michelle
I went in yesterday for my first prenatal appointment and ultraound. Going by my LMP I should be 7 weeks 5 days but dr didn't see baby or heart beat, just a sac. She says maybe I'm not as far along as we think and that's why she couldn't see anything. I've had no pain or bleeding and will find out what my hormone levels are today. Anyone else have something like this happen?