Ovulation Question

Hi! I am sort of new to all this and have been tracking & reading about TTC for a few months now. I typically am irregular (30-45 day cycle sometimes longer) but for the last two months it was 31 and then 32 days, but the app shows my fertile window starting right after AF. Should my fertile window be this soon (starting on cycle day 8)? I thought it would be around day 17-21? Thanks ladies for your help in advance. Also, during the window I didn't notice any significant changes in CM.