Computer excercises

Alot of us spend too much time on our computers.
Too much sitting affects my sciatic nerve on my left side and causes
a bit of discomfort in my lower leg.
It takes a huge effort to work that nerve back into its groove on the hip bone.
When I do get it back in the right spot, I feel great for about 3 weeks and it starts all over again.
Does any one know of any sciatic nerve manipulation techniques that might help?:smash:

Also, what other simple excercises do you do while at the computer to prevent getting stiff and sore?