Progesterone labs/pregnancy test question.

Michaela • I'm 25, Married, PCOS, Two angle babies, Delivered our twins 7/25/17 at 24 weeks and they are perfect 💙💙

I took letrozole days 3 thru 7, had an HCG shot 2/20 on day 14. I got my darkest OPK on 2/22 day 16. Went back 2/27 day 21 (yesterday) for progesterone labs. Got the call today saying the results were excellent. What is the earliest I should start testing?

I know it's best to wait until after a missed period but I don't have regular periods, I have to take provera to induce them.