To soon for US 😕

According to my last period I am 6 1/2 weeks. I had my first Dr appointment today and she did an US regular not vaginal. All she could find was the little circle, but could not measure anything. She didn't seem worried, said something about their US being ancient, but she is testing my HCG levels... had this happened to anyone else?? I'm sorta freaking out since I had a miscarriage in 2015 and we just now got pregnant again.