Hey Lynda,
It's nothing to stress over for now just relax and try to not have sexual encounters until you are ready for the possibility of a child. Maybe your boyfriend or yourself can go together to a pharmacy and one of you can get a test just to relax your mind. Wait a few days after your missed period and then take another one a week later. If they both come up negative then go to the doctors because you could have ovarian cysts or something of that nature. Also I have read studies that plan Bs can have a lot of side effects so I personally stay away from those. I also missed a period last month but had all the symptoms and wasn't pregnant so I will be checking that out. Period symptoms include (but not limited to): Swollen breasts, bloating, diarrhea, constipation, cramps, cravings, hot flashes. Pregnancy symptoms include (but not limited to): swoken breasts and areolle, cramps, dizziness, fatigue, white stretchy discharge, high cervix, fatigue. I hope you can get the results you want.
Good luck!