Progesterone test

Heather • so blessed to have my 2 beautiful children!
Has anyone ever had progesterone tested? I first read you should test 7 days before your period. The doctor told me to test on day 21. I told her my cycle is 24-26 days. So it should be 2.9-20 in the luteal phase ( the last 14 days of cycle ). I tested day 21 and I had 3.9! I'm worried is this too low? Yes it's in goal and yes it's probably 4-5 days late if my cycles is 24-26 days. I also spot a few days early too. I'm ttc past 10 months and I miscarried in December. I need an input. Thanks! ☺