Long hours sitting at a desk can cause pain and discomfort. A little preventive action can go a long way here is tip number one.
#1 Notice how the chair seat feels under your pelvis.
Is one hip carrying more weight than the other?
If so try putting both feet squarely on the floor. You may need a foot riser if your chair height does not match your leg length. Now push into the floor with one foot at a time to help redistribute the weight between hips. Recheck through out the day.
Also you can alternate between each foot, pushing into the floor to create a rocking motion while you are sitting. "A little walk while you sit."