Is there a chance of getting pregnant if you had sex a day before period? some doctors here said that it is possible and some are not. i need exact answer please.....?

There is nothing exact in this. Periods can vary in time and duration as can time of ovulation. The best way to avoid pregnancy is to use available methods of birth control and/or prophylaxis

Pregnancy has been documented from unprotected exposure on any day of your cycle including during menses, although less likely at that time.This would be more likely in someone with erratic cycle times and less so when they are quite predictable. Low means low, but that also means it is possible.

An exact answer does not exist. Pregnancy has been known to occur from sex on any and all days of the cycle. At the other end, even under the most optimal circumstances pregnancy occurs one third of the time from unprotected sex. If you do not wish to be pregnant, use contraception all the time, every time. You may consider implanted contraceptive, or IUD.