Cycle tracking and periods

TMI? So I’ve been TTC for 5 months, and my period was stable until last month. Last month it came in super weird for me. Spotting that started light and got heavy over 3 days. Day 4 needed a pad. This started a week before AF was expected. Again this month. My question is about tracking… when I spot for 3 days but not heavy enough that I need to use products, is CD 1 the first day of any bleeding or the first day of heavy bleeding? And then after a few days of heavy, it went to spotting again, for about 10 days total. Was that a 10 day AF? That’s not my normal. I’m trying to track accurately, but my body can’t seem to make up its mind. I’m concerned how this impacts my fertile window.