I have irregular periods and the other day i had brown discharge, i had unprotected sex the same day, what is the possible changes of getting pregnant?

Depends: It depends on your cycle (it's irregular, i know). If you had ovulated around the time of intercourse, you may have gotten pregnant. If the brown discharge represents a "period, " you're ok. Otherwise it's a roll of the dice, since you aren't regular. Did you use contraception? If not, please think about doing so. A home pregnancy test will let you know if you are pregnant. Check in about a week.

Pregnancy chance: Pregnancy chances will depend on ovulation and since you have irregular cycles it is hard to say. However, anytime you have unprotected intercourse you always have a chance to become pregnant. If you are trying to avoid pregnancy, you should use an effective birth control method.