It sounds like sciatica. Did you have any kind of injury? Ever get pain from riding a bicycle? I think mine is from periformis syndrome, but that's always a guess because it's virtually impossible to correctly diagnose -- it's more a process of elimination. Whatever caused it, go on YouTube and look for exercises to stretch the periformis. Even if you don't have that problem the exercises should help loosen it up. Hot baths in Epsom Salts helped me. Icing helps if it results from some activity you're doing. It could also be coming from the hip or the lower back. Again, look to what you've done lately and see if you can remember something you did that caused pain in those areas.