Very irregular period! HELP!

Casaundra • 26YO..1st BFP on 4/30/15..#3 for him..#1 for me..TTC since December 2014. Married 11/2013. NC 🎀
26 YO, no little ones. Since the start of my very first period around the 6th grade... I had never ever missed a single period until about a year a so ago! Now I never know when to expect my period! It only comes every 3-4 months! If we weren't  TTC this would be great..but now it sucks and I'm worried....
It may be important to note that I met my now husband 5 years ago and over these years I have gained approximately 90lbs...🙈
How am I supposed to know when I'm ovulating?
Has this ever happened to any of you? Was it ever corrected? How did you correct it?!