Was blood work done too? This could indicate thyroid, sugar, hormone imbalance, vitamin/nutrition deficiency as well.
If he did have blood work done and all the levels came back normal, I would find out if any of these levels were in the high/low range of normal. If so, then I would have him follow up with an endocrinologist. Which even if certain blood work comes back normal, but near high/low normal can still indicate a problem. Which is where the endocrinologist comes in at, they are much more knowledgeable when it comes to these.
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