Just a warning about "checking his thyroid." This happened to my own child.
A person can be hypothyroid while their thyroid is fine. For some reason doctors often just check TSH which comes from the pituitary. There are actually about half-a-dozen hormones to check. And, there are even reasons what looks like lowish but "normal" levels of T3 and T4 may not be sufficient - that it is not working well on a cellular level. Some reasons are antibodies, low vitamin D, low omega-3 fatty acids. Although this is about brain function, it might be helpful: http://itsnotmental.blogspot.com/2011/01/brain-health-thy...
My little girl had blatant symptoms of low thyroid yet we were told many times "her thyroid is fine." Yes. her thyroid was indeed fine. But she DID have low thyroid hormones from the hypothalmic-pituitary axis.
She also had low levels of some necessary nutrients due to a not being able to tolerate some foods.
Here is something one doctor wrote up: http://itsnotmental.blogspot.com/2011/01/childhood-onset-...
Of course, it may be nothing... just emphasizing that once in a while it *is* something, but the doctors are not looking in the right place.
Oh, and my little one also complained of her feet hurting - and over the years, ankles, knees, muscles... every small injury accumulated a new pain... her stomach, her head... and eventually it was all chalked up to the "depression" (MDD-Major Depressive Disorder) she was evetnually diagnosed with at age 9. But the depression, too, was just another symptom of the underlying problems.