Hcg not doubling ?

So I’ve been spotting the past few days on and off. Currently 6w1d.

Hcg 14th - 29908 (5w5d)

Hcg 16th- 44848 (6w)

Ultrasound on the 14th showed only a yolk sac.

My practitioner doesn’t seem very optimistic at this point due to my hcg not doubling, spotting, and no embryo).

I mentioned it taking longer to double once the number is higher and she disregarded that and said no they still want to see it doubling in that time.

Anyone have similar situations/outcomes.