How Do You Guys Stick to Your Plan?

I'm an 18-year old student playing small stakes games...Over 10,000-15,000 hands (combined), I've been a winner at .5/1 up to 2/4 at Party Poker, with about 5,000 hands at each level. Unfortunately, while PokerTracker says that I have a positive win rate, I am still very deep in the red when it comes to total winnings.

Every time I have a good couple thousand hands, I can't resist the urge to play well above my bankroll and skill level, going to the 3/6 and 5/10 tables--and my bankroll isn't even really sufficient for 2/4 (though it's so beatable that it hasn't been an issue over 3,000 hands). The end result are big losses at higher levels and a deflated ego.

I know that poker isn't a get-rich-quick scheme, but I can never resist playing for more--I dream of winning thousands a month and playing in the 300/600 games in a few years...unfortunately, I tilt and tell myself that a solid winrate at 2/4 can't afford me that (though I know it can, if I were to actually go a disciplined month).

Anyways, enough ranting...how do you guys stay disciplined and not take shots at levels at which you can't afford to play (bankroll-wise and/or skill-wise)?