How effective is plan b? saturday and sun i had unprotected sex multiple times with ejaculation inside me.. after the last time i took the pill

Most of the time: Plan B works most of the time, not all of the time. One should do a home urine pregnancy test 3 weeks after Plan B. Also, use reliable forms of birth control so that Plan B will rarely be needed (hopefully never) in the future. A person should only need Plan B zero, 1, or 2 times in a lifetime. That's for an entire lifetime. If the sperm last longer than the Plan B... then a baby is more likely.