Confused please help

Hey all im feeling pretty down in the dumps. I came off pill a year ago and my cycle had been a pretty consistent 28 days/give take 12 hours. Last month i was 30 days now this month 33 days. I really thought it had happend but then af arrived this morning.  I refuse to bbt as i know i will become obsessed. But now i just feel like i dont know when to do the deed for best chances. My app is showing 11!!! Purple days this month and i just know i cant keep up the energy for bd for that long. I just dont know when my most fertile days are goingnto be.. Feeling pretty depressed :(