I've Always Had Irregular Periods, So It's Not Unusual For

I've always had irregular periods, so it's not unusual for me to skip a few months here and there. That being said, recently I felt the oncomings of PMS (bloating, cramping, etc...) but it's now been three weeks since these symptoms began. Last week, I had sex with my boyfriend and the condom broke during intercourse and was not notice until after ejaculation. What are the odds of getting pregnant in this situation?