iPhone 4S Screen Blacking Out.

So just today my iPhone 4S screen keeps going black as if I locked the screen, but in a few seconds it comes back - this only happens on the home screen, so when it blacks out, the screen goes black then comes back on to the home screen as I left it. I've fully charged it, I haven't dropped it or gotten it wet. It just keeps blacking out randomly. I do have a case for it, but I don't think that could be causing it as I've had the case on it since I bought it and this issue only started today.

I bought my iPhone 4s at the beginning of December 2011 so it's new, and I'm not sure what could be causing this. Prior to my iPhone, I was an avid iTouch user and never had this issue, so needless to say it's a bit strange.

Any ideas before I go back to Rogers (my wireless provider) and see what they suggest? I don't have an Apple store near me and I can't afford to send it off to Apple myself. However, it should still be under warranty via my cellular provider.