I have no idea what is causing this but I think, given that the doctor, try as he might, has not helped that you need to branch out and start asking for second opinions and referrals to specialists. You've had an x-ray but, of course, there are more precise imaging tests that have not been run.
Neuropathic pain, if that is what you are experiencing, can be difficult to treat and it can take some time to find the right medication.
If you continue to flummox the medical profession you might want to try NORD, the National Organization For Rare Disorders, and see if they can give you some guidance. Good luck!
Here are some links that might be helpful in the meantime:
Nerve pain at a Glance
Neuralgia – An Overview
What Can Be Done for Nerve Pain?