My partner and I have been TTC baby number 3 for 9 mths now, my doctor has just requested the progesterone test to see if i am Oing but im confused he said to have it done at 21 days but my cycle is normally 37 to 40 days long which means by day 21 i wouldnt even have Od yet, i should O about day 24 correct? so at what day during my cycle should I have the test?

any help would be great. TIA.