Progesterone testing

My doctor wants me to go for my progesterone blood test to see if im ovulating i need to go 7 days before i start my period as i have irregular cycles which range from 33-45 days my predicted AF is to start on 29 june based on ovia app and 5th july based on glow app, glow is predicting on a 40 day cycle...the thing is i've started spotting since saturday cycle day 23 and im not sure if its my AF or what as its not full flow period bleeding just been spotting on and off since saturday now im confused as to which day i should go for my progesterone blood test in case my results come back abnormal as it happend once before, what should i do should i just go for the blood test based on my predicted period dates????