The sex was 1 to 3 days before her period. she did have her period but i read that she can still be pregnant if she has an irregular cycle?

Could be pregnant: The short, simple answer is that a woman can get pregnant at anytime during her menstrual cycle, even during her period, though that is less likely. The fact that your partner did get her period in just a couple of days is quite reassuring that she had already ovulated that cycle. HOWEVER, if you don't want a pregnancy, use reliable contraception every time. Good luck!