Can you have two periods in one month after taking plan b ? and will it effect me in any way took two pregnancy test both came out negative help ple

Yes, it can change : Yes, Plan B can cause some irregular bleeding after use. A neg preg test taken 2 weeks after unprotected sex should be positive if you are pregnant. If you have two tests neg., that's reassuring it thru were taken 2 weeks after sex. PlanB is very effective as emergency BC, and most effective eithin the 1st 24hrs after sex. You should be just fine. Keep track of your cycles.