If you have sex right after your period and you ovulate early that month, it's possible to get pregnant. This is more likely with. the time when a girl is most likely to become pregnant — can happen within a few days of when your period ends. Also, sperm can fertilize an egg for 72 hours (3. One of your ovaries will release an egg (ovulation) about 14 days before your period starts. The first day of your period, when you start bleeding, is counted as.