Progesterone RX - when to start it

After two consecutive MC (😓😔) I’ll be put on progesterone RX the next time I get pregnant. I’ve been reading lots of women getting on progesterone before they get a BFP. Should I be getting on it soon too? I’m 2DPO but it kind of sounded like my OB office wasn’t going to start me until I get a BFP? Should I call to clarify? Has anyone else been put on this RX AFTER they got a BFP?

I don’t seem to have a problem GETTING pregnant but it’s keeping it that’s the issue. I just want to give the RX as much time to work as I can.