" guess there is no way to pinpoint of what is making him feel better or worst unless I keep him on one supplement at a time.
"

Or perhaps just add or subtract one supplement at a time.

He is getting one teaspoon a day of cod liver oil? Perhaps you should increase that to 2 or 3, especially if he is not taking any other vitamin A or vitamin D. How much vitamin C is he taking? Is he taking calcium and magnesium? If not, then you should add it. Calcium can be constipating, so many suggest taking it together with the magnesium to balance it out(magnesium has a mild laxative effect in low doses). There are supplements with magnesium and calcium citrate together.

How is his weight? Overweight, underweight, or average?
You said his temperature is around normal? Mine is often below normal.