Some suggestions (without looking at your game):
1. Study lots of master games to see how they finish off their attacks.
2. Study books on attacking in the middle game (not just tactics).
3. Study books on positional play.
4. Study endgames.
These things should help you to become better at finishing off your opponents once you've got a good position. Actually, one more recommendation, which is porbably worth spending more money on than all the books covered in the last 4:
5. Get a master level coach, and have him look over some of your more frustrating games with you. Besides pointing out specific moves where you could have played better, he'll probably notice trends in why you're not spotting those moves, and can recommend specific books to study to help with your specific weaknesses.
I am USCF rated 1600, though I regularly beat 1700-1800's. I usually get a very nice position out of the opening; possibly even a winning middlegame position. And then, everything gets traded off and I draw. I've become very frusturated, because it seems no matter how good my position is, I'm not able to get that extra thrust of power to push it to a win. Observe one of my tournament games, played against a 2000 (!) player.
As you see, I was better the whole game, and unable to convert all my advatages into a win. Obviously, drawing a 2000 is good for my rating points, but I don't care about rating! I care about playing good, strong chess! And drawing is like a loss to me. If anyone has any thoughts on this matter, I'd love to hear your words of wisdom.