A doctor should always inform a patient if a medication is being changed. Perhaps, the doctor (or staff) made a mistake and was unaware of the switch.
On to the brain... the brain always influences pain. In fact, without a brain you would have no pain, literally. Brain damage, disease, or imbalances can absolutely be contributing to your pain experience. You might want to consider finding a neurologist (nerve specialist) who specializes in pain also.
Dr. Christina Lasich, MD