It may be as simple as attaining a lumbar support to retain some lordosis (extended curvature) in the spine while sitting. As a therapist myself, I would also consider deeper tissues, particularly your discs. They act like a water balloon in that compressing one side can form it to bias towards the other. While in most cases a temporary effect, prolonged sustained and/or repetitive motions can cause wear and tear and the remind may not be as effective. KStarr explains it well in his book. Fortunately, if you catch onto it early enough, you can easily reverse the problem by correcting posture and repeated extensions. Think of bending backwards while you’re standing out doing a cobra while lying on your stomach. Performing either every few hours and avoiding a sustained position for too long ought to help. Combining the mobility exercises per the links Kaitlin posted along with repeated extensions (~10-15 reps ) should help you on your way to recovery.