I need help figuring out my cycle

So I have endomitrosis... I didn’t intentionally get pregnant with my daughter... and I have been trying to get pregnant again but my cycle is so messed up I don’t know what to do if my fertile window is not accurate. 😕 I tried last month and I ended up getting my period 4 days earlier than I am supposed to and it didn’t work because it threw my ovulation day off.