in September and October I purchased plan B for my girlfriend she received her period.On both months after taking the pill. we had unprotected sex once in NovemberI went in for only two strokes and stopped. I did not ejaculate inside of her. she now says her period was light, spotty, and lasted less than 24 hours. she got it at the end of the month like she always does. should i be worried about pregnancy or is this just plan b altering her period? again she took it two months in a row. please help!