Baby number 2

Okay so a few days ago I found out I am pregnant with my 2nd child, I’m 5 weeks and 3 days and I’ve been having a lot of pain with this one so I went in for a emergency ultrasound and my sac is empty, they said not to worry because that is normal for 5 weeks. I’m getting very worried and keep looking stuff up in the empty sac and it’s not want I want to here. So has anyone else not been able to see the baby at 5 weeks but shows up later?