Yeah making sure everything is healthy, esp in someone irregular, is important. For example I had a giant fucking cyst on my ovary that I wouldn't have known about if it hadn't started hurting like a motherfucker one day (felt like very bad period cramps but in the wrong spot).
Guess what, no eggs from that ovary cause it was all blocked up from endometriosis. Whole thing was clogged with extra tissue and blood.
Also sometimes women start ovulating before the end of their period. Sometimes also women can tell when an egg drops if they have sharp pains around the pelvic area.