So after 2 years ttc I finally bit the bullet and went to see my dr yesterday, so I need to do a cycle day 21 blood done followed by a cycle day 2 blood test, what I want to know is I have a 26/27 day cycle and she said that the progesterone surge only happens for 24 hours and it’s very important we catch it so how do I work out my cycle day 21 when I don’t have a 28 day cycle, does it go by ovulation etc? Sorry if this is a stupid question but I’m new to this and I want to make sure I don’t miss it 😢