It sounds like you have a condition known as Sciatica. I've had it for years. Go to your doctor and ask for some medication. However, if he offers you Diazepam ask for something different. Diazepam relaxes the 'muscle spasm' which is what you are getting, but it makes me (a) VERY VERY tired, dozy, causes forgetfulness and all sorts. Why the hell druggies use them I just don't understand!!
I have suffered back pain since I was 28, I'm now 53 and they STILL don't have a name for my condiotn...(Perhaps I will be come famous?? lol) My spine is breaking up and they just don't know why. I was always short, 5.6, now I'm 5'4 and still shrinking!!