Low progesterone - Am I being tested on the right day? Please help!

[babywhen]

A bit of background - I'm 33 and have fairly regular periods usually (30-34 days). Since March, they've been every 40 days.

I had the progesterone and other hormone checks done on Day 21 and it was very low. Had it again on Day 21 of my next period and again very low so not ovulating. However, I've since read that day 21 is only accurate on a 28 day cycle.

Is there a possibility I am ovulating but later on? Or should my progesterone still be higher on Day 21?

You should have your progesterone checked 7 days before your period is due X good luck x