Usually when taking plan b my period comes. this time it didnt. is it normal or does that mean it did not work?

Usually: Usually, Plan B is taken to prevent pregnancy in an emergency situation. I strongly discourage people from using it as a routine contraceptive. If taken as directed, it should work. If not sure, get a pregnancy test.

That may be a Plan B: side effect. Potential side effects w emergency contraception includes menstrual flow changes (spotting, bleeding, early or late period). If you are regularly using Plan B - than you are misusing it. It is not meant to replace regular, consistent birth control.