Considering you and your boyfriend have been doing the horizontal jog without protection for a month, there's no telling when you could have possibly conceived because there's no way to tell when exactly you would have ovulated. I'd say you have a pretty good chance of being pregnant, but maybe lady luck was on your side. You could be anywhere from a few days to a month pregnant, and symptoms will show up no earlier than a week past conception.
If you're freaking out over this, your body could be convincing you that you're pregnant. Women may have pregnancy symptoms without actually being pregnant when they either really don't want a kid or they really do.
In the event of pregnancy, are you guys going to attempt to be parents? I don't mean to sound discouraging, but a lot of guys will say they'll stick by their girlfriends when a baby is incubating...But when it arrives, they suddenly don't want to be fathers yet. Teenaged boys rarely are ready for parenthood, so don't be surprised if he bails out one day. This all applies, of course, if you plan on keeping the thing.