I know that day 21 progesterone testing is usually to determine if you ovulated. I also know that if your cycles are unpredictable, sometimes it's better to do P testing 7 days after your actual ovulation day, and not just the default "day 21."

Three questions:
- Would day 21 progesterone testing be a way to backwards determine a better estimate of when I ovulated? I think I either ovulated day 13 or day 16. Could I go for the default 21, find out my level, and be able to better det. O date?

- If your day 21 falls on a Saturday, would it be better to do day 20 or day 23? I think day 23, bc of the possible late O?

- How does taking Prometrium figure into all this? I was supposed to start it after ovulation, but I haven't yet bc I'm not sure if I O-ed yesterday or not. I'm thinking of waiting another day or two, like day 18 or 19.... does it artificially inflate P levels?

I know I could ask my OB but for various reasons I'd rather ask all of you