My bf & i had sex while i was ovulating he cum inside me the next day i was already on my period so i took plan b, the next day he cum inside me again?

Doesn't make sense: Your question states that he ejaculated when you were ovulating, and then next day you were on your period? Ovulation and period are 10-14 days apart. Bottom line, if you're having sex and don't want to be pregnant, then a reliable birth control is better than plan b. For Plan B to work has to be taken immediately after sex and every time you have unprotected intercourse.