Hello, thanks for your query, For someone to get pregnant, first of all there must be fusion of the male s gamete and that of the female. For that to occur, the male must ejaculate in the female who must be in her fertile period. With an irregular period, getting the fertile period could be difficult but that does not rule out the possibility of getting pregnant. Ovarian cyst does not prevent pregnancy unless you have what is known as polycystic ovarian syndrome which occasionally prevents ovulation thus causing infertility. Taking contraceptive to prevent pregnancy can only work when taken within the first 72 hours. You took th epills 4 days later, thus there is a risk of getting pregnant if you were in your fertile period. You will need to do a pregnancy test 4 weeks later or meet a doctor for further clarifications. Hope this helps. Dr Achuo