How can I get rid of back pain without forking out money for a masseuse?

I’ve been having terrible (sometimes debilitating) cramps in my back of late, especially my upper back, and sometimes my neck. Every time I stretch (like standing erect after sitting at the computer, or simply tilting my torso from side to side), my back cracks a bit more often than I think it ought to. I’ve felt my back muscles, and all up and down one side it’s hard as a rock.

I’m a lad with very little pocket money. What’s a simple home remedy I can do, or some sort of stretching technique/self-massage I can do? Maybe it’s the way I sleep?

I’m only 24 years old, I shouldn’t have back problems already, right?