FAM Method

Okay so I stopped taking birth control and wanted to be more on the natural side of my health. I wanted to learn how to efficiently track my ovulation. I'm on a budget so I can't go out and buy a tool that's $300 either. First of all, my period is irregular, I've been tracking it but it isn't consistent so I don't even know if this method is right for me. Can I get some advice or tips as to what you guys do?