I have one large ovary then normal size. does this cause irregular period? will it cause any problem if i want to get pregnant?

Yes: You may have a polycystic ovary which causes the ovary to be larger. It may cause you to have an irregular cycle as it can cause hormonal imbalance. It could interfere with normal ovulation, but does not prevent pregnancy. See your Provider and check it out!

Possibly No: Size of ovary has little to do with getting pregnant unless one has a pathological condition associated with ovaries like Polycystic Ovary Syndrome, which can cause irregular periods and for which you can get your hormones checked for proper management