Progesterone Testing, Day 21-23

Hi, everyone. My husband and I have been ttc since September of last year. There were a few months we didn’t try due to a trip to Jamaica that caused us to have to wait. So, overall, not quite a year of trying technically. We had a miscarriage in May, and have not conceived again. My doctor has asked for us to wait 3 more months of trying on our own until we come back in, and has ordered progesterone testing on day 21-23 of my cycle in the meantime.

Who has experience with this? Did it help? Sort out any problems? Just trying to learn how common it is. Thanks!