If i have unprotected sex three days before my period what's the chances of me getting pregnant ?

Possibly: Unfortunately, there is always a chance of pregnancy with unprotected intercourse. Being prepared with some form of contraception will be your best weapon to avoid pregnancy if that is what you wish.

Low.: It is not likely that you will get pregnant from a single unprotected sexual encounter on the 25th day of a regular cycle - however keep in mind that ovulation does not always occur on the 14th day as it is supposed to! use some reliable form of contraception (iud, ocps, dmpa) - the cycle method is notoriously unreliable. Take 1-5 mg of Folic Acid daily just in case you get pregnant anyway.