Suggest Treatment For Severe Headache

Question: My husband got flu like systems on way home from Alaska three years ago. He recovered & a week later developed the "most severe headache he had ever had" The right side of his face started drooping & the uvula swelled twice it's normal side, so we made a trip to ER where they did a cat-scan & other tests for a stroke, etc. All tests were negative.
The initial systems eventually left but he was left with hypersensitivity on his right side.
He has had nerve testing, heart tests, MRI on head & neck. All tests have come back negative even though his neck MRI did indicate there could be slight arthritis.
In the meantime, he had to have a total hip on his right side & also a torn rotator cuff on the right side.
We were hopeful that the pain would ease after those repairs. The arm & hand have continued to tingle & burn.The leg has been the most painful & had switched from tingling & burning to deep muscle type pain.
That is the most excruciating pain.
Having said all of that, I am asking for insight as to what type of tests or Doctor we should seek in order to get to the bottom of the condition.