Firstly, congrats on your pregnancy.

TBH, I'd go to another obstetrician if he doesn't seem to know much about progesterone. I needed progesterone with DS3 and (in my opinion) it was the difference between miscarrying and maintaining the pregnancy as it was rather touch-and-go for me in those first few weeks with my progesterone continually dropping until I started on the pessaries. And once I started the pessaries, my pregnancy settled and continued on to be a very healthy one.

ETA - I realised I'm not addressing your initial query, but I kind of felt the need to comment on your remark about your Ob. Hope that's ok