And I am 99.9% sure you are not pregnant it's nothing to worry about unless you are doing it all the time. In that case the probability increases.
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 and 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. I hope you can get the results you want. Good luck!