Good evening everyone!!! I'm at week 7 of pregnancy, but according to …

Good evening everyone!!! I'm at week 7 of pregnancy, but according to ultrasound it's week 5 with 3 days. We have an ultrasound check-up in two weeks. The heartbeat wasn't detected, only the yolk sac was shown and that's all. Is this normal? I'm worried... Has anyone had such a situation? Thank you)