Pregnant

So about 2 months ago when I went home for winter break, I had sex with this guy I use to talk to before I left for school. Well long story short, after that night we never had another encounter, it was just that one time. Now present time, I’m about a month and 2 weeks late for my period. I took a pregnancy test last week and it came back negative. I went to the doctor to double check and he said I wasn’t pregnant. I’m on birth control and he always pulls out, but I’ve still yet to get my period. I get the camps, the mood swings, and all the other symptoms of a period. I have experienced any pregnancy symptoms. Idk what to do and I don’t want to start stressing. Somebody tell me what to do.