High hcg but only a sac on US. HELP!

So I thought I was 7w6d pregnant today according to my lmp. I went to my appt today and they only found a sac in the vag. US. No baby in sight. We took another hcg blood test and it came back at 33,756. Two weeks ago it was 1,832. I don't know what this means. Before the blood test came back my doc wanted to do an us in 10 days. But after it came back she said she was surprised the blood hcg came back so high today and my doc wants to do blood again in 3 days along with a more elaborate ultra sound test. Has anyone else had anything like this?