Need help tracking ovulation

Okay guys I need your help. I'm ttc but can't track my ovulation days. I was on the depo for nine months and then stopped. I quit the shot in April and got my period back in september. They are back but still not regular. Last month I got my period at the beginning of the month and this month at the end. I've been taking ovulation tests but I'm wasting too many with my period irregular I'm not sure what days I need to be testing. Can anyone give any type of advice? I would really appreciate it. (: