Going crazy

Fillegirl25

I went today hoping to see a sac on the ultrasound. My betas have been doubling but on the low side... 60, 197, 457. My lining is super thick, Dr. said "there is something in there" but no visible sac. They keep telling me its early. With my son I had already saw a sac at this point., 5 w, 2 days. They said every pregnancy is different and don't compare.They tell me 1500-2000 beta is the point where a sac is seen. I SHOULD be close to 1000 today. They checked for bleeding, inflamation and saw nothing. Where is it and why is this so nerve wracking! I feel like my breath is held....I hope to exhale soon! Does this sound right?