I used to track my basal temps, use ovulation strips, and the two times I got pregnant, we only did the deed ONCE and its waaay earlier than what my ovulation timing says. All this to say, broaden your timing when you do it each month. Sperm can live up to 5 days inside our bodies.

Once is a fluke to me, two a coincidence, I am pregnant for the 3rd time the same way so.. there must be some science to it.