More than doubling HCG?

Emily

So I'm not sure how far along I am but I went in for an ultrasound last Wednesday and the doctor didn't see anything. She sent me for blood work Wednesday and Friday. I got my results back and on Wednesday they were 2,907, Friday they were 6,794. 156% increase 😳 I go in for another ultrasound next Wednesday. What do y'all think it's going on?