please leave advice and help !

help!!!! about two months ago i took plan B i bled right after and then after that (month later) had my period. took a bunch of test to make sur i wasn't pregnant. here i am now two days late, haven't taken a test but that was the last time i had unprotected sex and i had a period after , indicating i wasn't pregnant. does plan B mess with your cycle for a few months?? i've also been taking acne pills and think that could have messed with it ?!? i'm freaking out that i'm pregnant but i try to think that like i've taken about 8 test and all negative since the incident. anyone have this experience with plan b?