missed my period? struggles of irregular

Grace • Australian • Married • TTC since October 2016 • IVF WARRIOR • " Never let odds keep you from being what you were meant to be "

How do you determine when you have "missed" your period if you have an irregular cycle and cant seem to get accurate readings on opk's... last month i had a 31day cycle and now i am cycle day 33 with no AF but cant determine if im "late" or its just not due.