lower back pain: what excercises?

I'm 18 years old and experience lower back pain after 3-4 hours sitting in front of my computer. Especially the right side of my lower back..I think the muscles on the right side of my back are a bit less developed than the lower back muscles on my right side of the back.

That said, do you guys know any excercices that might be good for my lower back?
I don't have weights so exercises that you can do with just your body weight would be cool.

http://athletes.com/fun/exercises.htm check this out,