Treating chronic leg/back pain

I've been suffering with a sciatica type pain in my left leg for around 4 years. The intensity of the pain varies, but it never totally stops. It's at the almost unbearable stage right now, and affecting my whole life.

I've had numerous tests and scans and a nerve conduction study showed compression of the L5 nerve. The site of the compression can't be found, and scans show my spine to be in good health.

I'm currently having spinal steroid injections, but the effects are short lived. At the moment i'm taking some heavy duty painkillers, but they don't have much effect.
I've tried everything i can think of, including Osteopaths, chiropracters, and accupuncture.

Has anyone else had a similar problem, and managed to fix it?