I've never quite got that drinking water makes one feel full because it doesn't hang around in the stomach for anywhere near long enough to make any difference to me beyond about 20 minutes. Mind you, I drink tons of water, and can't say it makes me feel hungry either.
Try sipping your water over a longer period of time, rather than downing large amounts at once. This should help eliminate the stomach ache, especially if you drink your water very cold.