Talk to Neuro Physician on Diplopia / Muscle Weakness

My acquaintance has developed diplopia 9 months ago along other symptoms like nausea, dizziness, numbness and tingling on one side of body with jaw and teeth pain. Neck stiffness and constant fatigue. These symptoms come and go in episodes and become worse in hot weather with hives. Been to multiple doctors and still no diagnosis. Brain MRI was clean and ophthalmology keeps on changing the number to resolve issue but no luck with double vision. Anyone can suggest which doctor to goto to get it diagnosed properly as symptoms are becoming frequent