I was on birth control but not having a period so I stopped taking it for month and had my period. I started a new birth control pack the following Sunday after my period ended and had unprotected sex the next day but used plan b within 3 hours of the mishap. It's a week later and I'm cramping but my period isn't supposed to come for at least another week, if I have it at all while on birth control. Should I be worried?