Low progesterone

How many of you treated yourself with OTC low progesterone cream in order to achieve pregnancy and was successful? What did you do (as far as progesterone) once you go that BFP???
My doctor has me on clomid for my progesterone/ovulation and it was successful but unfortunately it was ectopic. She claims it was probably due to low progesterone which affected my egg's motility. Now I am able to try again and she wants to go back to doing the same exact thing only prescribing me progesterone AFTER I get a BFP. Why would that make sense if implantation would have already occurred at that point. It makes more sense to me to start after ovulation but before I get a BFP.