HCG Levels

My first pregnancy ended in a miscarriage, so my OBGYN always does blood draws in the beginning of a new pregnancy. My 2nd pregnancy was successful and I have a little boy. Last week my first draw at 5w3 came back 6568, but my draw at 5w5 only came back at 8786.

I have an U/S scheduled for tomorrow morning, but it doesn’t sound promising. Has anyone not had their HCG double within 48 hours and still had a successful pregnancy? I have read that once levels reach 6000, they can take up to 4 days to double, but I don’t know the accuracy of that research. I am currently still experiencing fullness, all-day nausea and breast tenderness. My app shows that I would be 6w1 today.