Hcg level not doubling but rising

Hi, I'm a little worried and looking for some positive stories or hope.
We got pregnant from <a href="https://glowing.com/glow-fertility-program">ivf</a>, betas were doubling every 48hrs. Then my doc pushed our third beta to 7 days after the second. My levels aren't doubling at all. Rising, but not doubling. My (jerk) nurse told me to be cautiously optimistic, and left it at that. I feel sick with worry. I'm 5w1d. I feel like I might demand an ultrasound tomorrow.
Anyone else experience this?