What Causes Inconsistencies In Periods?

I have a weird period. Ever since I stopped my birth control about a year ago it's been very strange. I might have my period two months in a row or I have to wait for 3 or 4 months. My husband and I are trying to get pregnant, but we can't seem to get success. I don't know how to determine my ovulation days with my period so out of wack...HELP!