HCG was doubles and then slowed down at 5weeks

Hello out there! Just wanted to see what people’s experiences have been. I found out I was pregnant after (2.5 years of TCC). My first HCG was 144 at 4w1d. 2nd HCG was at 650 at 4w4d. My 3rd was at 2396 at 5w. So it was doubling just fine. Then I went in at 5w5d for an ultrasound and they found the sac and yolk sac and maybe a fetal pole but it was too early. However, my HCG was at 3543 after 5 days. My doc is worried but didn’t want to say it was marriage but wanted to prepare myself. Has anyone had this issue where the HCG slowed down after doubling really well?