Quite often disk problems present themselves in ways that aren't really painful or an obvious back problem. It may very well be this isn't your problem but it is good to keep it in mind and check it out if other methods don't address it.

Yoga and Pilates are both good, as others have mentioned. Is your work environment such that you can get up from the desk every hour or two and do some simple stretches or something? Personally I have found that air squats really help me out when this happens.