jingl 
I think you may be onto something there. Went for a good long walk with a friend today, hoping that the walking might loosen it up (the pain, not my bottom) but was a bit though going at times, especially up hill. The went to collect tablets and have made an appointment, but couldn't get one until3rd June 
However, they did say if it is still painful next week, call each morning around 8.30 and if they could squeeze me in they would.
I'm pretty certain it's NOT my back, have had sciatica in the past and this isn't even remotely like it.