My boyfriend and I always use a condom when we have sex. Despite that I consider myself an intelligent person; every few times I convince myself I am pregnant. Though I'm fairly certain its false, my stomach feels strange, but not crampy; this is probably self-induced from thinking about it. Every time I think "I'm just being dumb" another voice says "but what if you are pregnant?"
The stress has made me late once or twice, and I find it hard to concentrate without becoming panicked. I have had several close friends have accidental pregnancies and it has made me even more paranoid.

I don't want to have to go buy a pregnancy test every few weeks because frankly that's stupid, and often I become this way with still weeks left till my period is due.

What can I do to ease my paranoia? I have school work to do (I'm 18 ) and I don't need this extra pressure.