Hi.
First, let me give you strokes for taking responsibility once you'd had unprotected penis-vagina sex.
And let me now put your worries to rest. Plan B is a big dose of hormones all at once, And it often causes unpredictable bleeding and periods for a little while after use--not just right before your period, so relax. However, JUST TO BE SURE, why not use a home pregnancy test to set your mind at ease? Of course it goes without saying, that if, after your period arrives, you continue to experience irregular bleeding, you should see a gynecologist.
And no more unprotected sex! You should know that the fluid that the penis secretes PRIOR to ejaculation can contain millions of sperm, so regardless of whether he ejaculated inside you, you could still have become pregnant. Time now to investigate birth control/risk reduction options and choose the ones that are right for you! Best of luck to you. Dr. J