How soon after you’ve finished your pill pack does your period start?

I’ve been on BC for PCOS for 9 Yrs. I was always on top of it and would always get my period on a Wednesday so about 4 day on the blank pills. As I have gotten older an have changed brands over time I have noticed my period starting either on a Tuesday or sometimes as late as a Friday. I’m thinking because I am a lot older now, stress or maybe my body is over the pill. Idk who knows lol