Confused

My HCG levels started out low....first 79 then two days later 119 and two days after that 133...the doctors told me that it is a bad pregnancy, but then at the next two day check up they took my blood and did an ultrasound....only to reveal nothing on the ultrasound which would not have been seen either way because of my low levels but then my blood work comes back at 420. I have another two day follow tomorrow, I am nervous and scared and confused. I don't know what to think about this. If my levels go down its a bad pregnancy but if they increase appropriately I have to continue to be monitored. Is there anyone who has had a similar experience?? Please tell me your story