Irregular periods!!!

Erin • 4 and 2 year old boys and a newborn baby girl
My periods seem to be irregular, some 5 days late and others 11 days late. My husband and I have been ttc baby #2 for 3 months, with no luck. What is the best way to track my ovulation so we can expand our family? Our first boy is 11 months old, and I would love for him to grow up close with a sibling.