Help or advise?

My cycle 31 days on my last 3 month of clomid dr wants to do blood test on 21? So do i take blood test befre i take clomid or should i take clomid first? Soŕry if im annoying last time dr didnt do any blood test so i am confused😯 please help ?

Wen should i go for the blood test if i had period on 17 may? And cycle lenght is 31?