First thing to remember, is that these voices have no power over you, they can't hurt you, you could say it's just a lot of talk - trying not to think about it can in fact cause it to continue or get worse, establishing an obsessive compulsive loop.
Schizophrenia involves what you might almost call a physical breakdown of the barrier between your conscious and subconscious/unconscious mind - neurons start firing at random, and consequently making random associations - your doubts and fears are crossing the limnal barrier while you are awake.
Try to relax and not worry about it, find some organized activity to engage in. Trust the evidence of your senses, and take it slow, it can be a hairy ride.
You sound too young to be experiencing a schizophrenic episode, but i'd definitely consider seeing someone if the stress is getting to you, and i'd be remiss if I didn't suggest you do so anyway, just because it isn't typical doesn't mean it isn't happening to you.