Sounds a bit like the sciatica I had a couple of years ago. The doc gave me a good test for it. You lie flat on your back and, keeping your leg straight and your ankle bent (ie toes pointing to the ceiling), raise the leg slightly on the affected side. If it's sciatica, it'll be agony. I was told it's partly caused by postural faults and can be relieved by correct posture. What causes the pain is a trapped sciatic nerve, so that fits in with what flobadob says.
And yes, impersonal or otherwise, doctor knows best.