High hormone levels without finding a gestational sac on ultrasound raised two possibilities. One is called an ectopic pregnancy, which is where the fertilized egg has implanted somewhere other than the uterus (most commonly the fallopian tube, but could be elsewhere). Usually, these have to be therapeutically aborted because they cause significant risk to the mother (ie they could rupture the fallopian tube). Another option is something called a molar pregnancy, which isn't a fetus but rather a growth that produces the same hormone as a pregnancy (a kind of tumor, sort of). Both should be further investigated.
I had this problem before...come to find out the baby was growing in my tubes.... miscarriage followed but not every woman bodies are the same...not to panic it is not uncommon just take it easy until the next appt....it will be ok.