Progesterone issues

Rachael • Married to my wonderful wife, mom to D, twins on the way. lots of other roles and titles.
Hello everyone,
I'm 12 weeks tomorrow. My RE is still monitoring my progesterone. It had been between 18 and 22....up and down again. This past week when it was 18 my doctor had me decrease from 1.5 cc to 1 cc. They tested today (5 days later) and it's 14.8. They're not worried and said to stay on 1 cc for now. I'm so worried about miscarriage and also don't understand why my placenta isn't taking over.Has anyone been through this??