My son is 24 years old and suffers from fatigue, generalized pain, headaches throughout the day and night. He is able to work full time as an engineer for the past 16 months, but it is becoming increasingly difficult to function normally. He does not drink, smoke and does not do drugs. He has no symptoms of depression that I can see. He is on a high protein, low carb diet for 6 months, lost 20 lbs and still does not feel better. He is not overweight. BMI is 23. Blood work showed cortisol WNL but precursor to cortisol was very high. What kind of doctor should he go to?