I Had Back Surgery In Feb. This Year Spinal Stenosis.

I had back surgery in Feb. this year Spinal Stenosis. I still have pain going in my left buttock and down the left leg. I feel like I am losing my leg. The pain does not get any better. My back has gotten much better still some pain but I don't know what to do about the butt and leg. My doctor said it is not coming from my back. What can it be?