Help- doctor says to do day 21 test

[Sahbahtah]

Hi help needed please!
My doctor told me I should do a 21 day blood test but that day 1 would count after I've finished my period.. I've been reading online that day 1 would count as the first day of my period so I'm unsure as to when to get the test done now? My periods come 1-2 months and I have pcos does that make a difference as to why my doctor said I should do the test 21 days after I've finished my period?

Day 1 is the first day of your period. PCOS shouldn't make a difference, I imagine your doc just got it wrong.

You're right - day 1 is the first day of your period.

The day 21 test is to check that you're ovulating. It should be done midluteal phase ie 7 days before your period comes. If you have a 28 day cycle that will be day 21, if it's a 35 day cycle then it's done on day 28.

Oh okay thank you both :) although mine usually come a week or 2 late and sometimes even 2 months later so should I just stick to day 21