Pregnant & only 17?????????????

I'm 17 years old & have been with my boyfriend for almost two years. I am on birth control but I was on antibiotics about 2 in a half weeks ago & didnt realize that it could mess up your birth control well we had sex & he didn't pull out. My last period started may 18 & I haven't had one since. I haven't really had any symptoms of being pregnant except for being more tired than normal. Also around the time I was supposed to start my period I cramped for about 5 hours but nothin since then does it sound like I'm pregnant or am I just stressing it?