If you're trying for a baby, have sex with your husband the day your period ends and then every third day after that, until the next period comes or you get pregnant. Sperm can live up to 5 (some research says longer) days in your body, so if you have sex every three days you'll cover the bases. You don't have to have sex on your period, it wouldn't do much good because right before the period is about your least fertile time and the period itself might wash a lot of sperm out. You only ovulate once a month and it is not during the period.