Low HCG, but doubling. Thoughts??

Hi all! So I had a m/c back in May and I am pregnant again. I’m pretty nervous and anxious around this one. The doctor says my HCG is still really low and can’t say if this pregnancy is viable or not. My first U/S is Nov. 5th. My cycles have been around 35 days so according to my LMP I’m 6 weeks, but I ovulated late.

12dpo-27 hcg

14dpo-67 hcg

18dpo-666 hcg

Every now and then minor cramping or low back pain. Other than that not much. I’m pretty concerned.

Any feedback is appreciated :)