Perverted Thoughts

I had this same problem. It took years to overcome and every now and then I might experience a bit of recidivism. What I started to do was getting off the computer. I find it when I'm alone and on the computer, the temptation to jack off is irresistable, therefore I just leave the damn house and find something to do. Be it to go to the library, a cafe, a bookstore, run around the park, etc, just choose your poison and go with it. When you come home, it's less likely that you'll feel the urge.
I also know for a fact that I feel absolutely drained and unable to do my daily tasks after a bout of this. I'm sure too much of the release of hormones during an orgasm is bound to change the chemistry of the brain over time. Sometimes I feel unable to feel any other kind of pleasure, irritable towards others, etc. You talked about the same things so I'm sure you know about the "side-effects" of masturbation first hand.

Tips:
-I know you have a folder with at least 10 gigabytes of porn in it. Trash it.
-Call up a girlfriend. It sounds simple or nerve-wracking depending on your mood, but try it sometime. It's soothing to be talking to a girl, hearing her laugh, etc.
-Hang out with friends. Go to the movies or something with them, just hang out and enjoy yourself.
-Yes, start exercising. Not only does physical exercise release these feel-good hormones so your mood is far away from the thought of jerking off, your health in general improves as well. I would start off by running, doing some push-ups or pull-ups if you have access to a bar, and maybe some lunges up a sweep hill.
Last but not least, don't feel self-conscious about improving your situation. A lot of people go through these but don't share it on a forum or anything. Just go at it with confidence, and I'm sure people will be noticing the change in your behavior. If it's positive stick around with them, if it's not just move on.

Jam it back in, in the dark.