How do I know what’s even going on?

My last 36 cycles have all been completely different some 47 days, some 28 days, my periods have been as short as 3 days and as long as 7 days. Apps can never predict my ovulation date correctly and no matter what tests the doctors do, nothing is the cause of these irregularities.

I’m at my wits end we’ve been trying since early 2018.