Last month my new boyfriend and I had sex and the condom broke. The next day I bought plan be and a week later I had my period. That period was lighter than normal. I haven't had my period this month at all, and we've been very responsible, using a condom every time, and another condom has not broken since the first. Is plan be messing up my menstrual cycle?

Plan B can and does have effects on your cycle.

Also of course plan B is not 100 percent effective.

Most likely it is merely the effect of plan B, but you will have to wait and see