Why is my HCG not doubling lately?

mom*may’18#😍

My doctor has been asking me to taste beta hcg test over and over and I am worried something is wrong

Aug 27th - 9.13

Aug 29th - 34.10

Aug 31st - 68.10

Sept 7th - 599

Sept 9th - 924

I got pregnant right after stopping birth control, so I am really really worried something is wrong.