Do you exercise? If not, it might be a good idea to start
I used to have the same problem because during one period I was spending a lot of time a my computer. Then I joined the gym and the exercises I did strengthened my back and helped me a lot! As well as doing some stretching exercises.
This is what I've come up with a google search, I've tried some of the exercises they mention and they helped,..google a bit more and try it out, see what works for you and what you can do at home.
Slide show: Back exercises in 15 minutes a day - MayoClinic.com How to Exercise While Sitting at Your Computer - wikiHow