the day before your period came, the chances would be much less, because you wouldn't ovulate right before a period. But a woman can ovulate as early as day 8 after her period starts, and sperm can live 4-5 days in the woman's reproductive tract. If you are within the 72-hour window, I'd consider Plan B.
, then ur possibilities of pregnancy are very slim. Women need to ovulate in order to get pregnant. A woman's monthly cycle is measured from the first day of her menstrual period until the first day of her next period. On average, a woman's cycle normally is between 28-32 days, but some women may have much shorter cycles or much longer ones. Ovulation can be calculated by starting with the day the last menstrual period (LMP) starts or by calculating 12-16 days from the next expected period. Most women ovulate anywhere between Day 11 - Day 21 of their cycle, counting from the first day of the LMP. So in ur case NO u would not be pregnant. If u want to be sure, take a pregnancy test. If u don't want to be pregnant, u should use condoms