A Pain in the Butt. The simple answer is to get up and move around if possible. Sitting all day on improper seats can irritate the sciatic nerve as well as the coccyx or tail bone. Coccydynia is a painful condition of the tail bone and the bursa that may respond to injection therapy. Sciatica requires relief from compression. Keep a wallet in the front pocket. Vascular claudication is a also likely possibility.
Try stretching, etc. If your job requires sitting all day, it might help to stretch, and move your body in the opposite way that you move it when sitting down to work. This would not only be likely to help the buttocks, but also your lower back, a true example of a place where chronic pain occurs. Lying on your stomach, and/or some swimming may also help.