Back pain problems - please help?

There's a particular spot in the middle of my back bordering right up against the left side of my spine that has been somewhat bothersome for a couple of years now, but lately it's really been bugging me. When I'm just sitting around I'm often compelled to put pressure on it in the same way that I'd be compelled to scratch an itch, and when I press on it or rub it with my finger, the sensation is sort of a pleasurable not-quite-pain - the sensation is more powerful than when I'm not touching it, but when I stop manipulating the spot there's no relief at all. I want to say it feels like a very localized pinched nerve, but I've read the symptoms of pinched nerves and they just don't fit at all. I think I want to say that because it feels like that spot is constantly being pinched a bit. At any rate, it's a constant irritation. Does it just sound like a bad knot in my back or something else? Any suggestions for how to get rid of it (I realize that it can't happen overnight) or to at least ease my discomfort?