3 months TTC ovulation test question

Hi all,

My husband and I are going into month 3 of trying to conceive. My period has always been fairly predictable 4 days, heavy first day, but I think this change is messing with my hormones because Last month I was 3 days late and AF only lasted a day and a half. AF showed up yesterday 2 days late 😔 and is super heavy this time around. I have no idea when my actual ovulation date is anymore. So I have decided to try the ovulation prediction strips. When in my cycle should I use them post AF? Any help would be appreciated 😊