So nervous!

Today I go in for my 2nd round of blood tests to see if my HCG is doubling. I thought I was 5-6 weeks but when I went to the doctors he couldn’t even see a sac but he did say there’s definitely something going on in there he just can’t see what it is yet. Said it might be too early but I’m nervous that I may have gotten pregnant but it didn’t develop or stopped developing. Praying there is just a mix up and I really am just too early. My HCG levels were 247 two days ago. Has this happened to anyone else and everything was fine?