Sounds like siatica
Pretty much only time can heal it - I thinks its kinda defined as irritation of the siatic nerve.
Pain goes from like just above bum cheek, to a point down the leg?
I think there are some physio exercises that are supposed to help but I don't know if they are much good.
Trouble with siatica is that it comes and goes and to relieve it you need to take the pressure off the nerve (when you stand or lay straight).
Can't think of much more off the top of my head about it now, will keep thinking, but someone else might come up with something.
Try relaxing - nice warm bath, or maybe a massage - but not a deep sports massage