How Can Irregular Periods Be Regularized For A Successful Pregnancy?

my periods have been very irregular since january i got it on january on the 24 finished 31 february 28th finished on the march 6 april 6th finished 12th May 23rd finished 29th may july 7th finished 13th july how long is my cycle am trying to get pregnant but dont know when my ovulation days are. Please assist me