To those with pain in the ... buttocks, I would say it is probably sciatica (non-medic, speaking from personal experience). Do what most of us do, grin and bear it (especially if you have hit middle-age) and don't spend money on physiotherapy. It does go away some times. I used to get it a lot many years ago when I was driving a car with a very soft seat. A firm seat felt much better.
ydt