Get him checked!
Most of us have a friend, neighbor, etc. with a small machine that tests blood
Sugar with just a prick of the finger. Ask everyone you know, someone will help you on this. Or call your local hospitals. One of them may have a clinic that does this for free once a week or so.
Immediately begin keeping a journal of all his symptoms, with age, weight, other health problems he has and you and his father have in your family and post those here to see if you can get a better idea of what's wrong with him. Read the
Iodine VWT forum. Some of them have had good results with their kids.
Don't hesitate to take him to a doctor for a blood test. A lot of things can make one tired. Doctors are very good for diagnosis.
Although theoretically, give the body what it needs and it will heal is great, it helps to know if he tends to diabetes, leukemia, a diseased heart, or pinworms.
Don't let this go, for his health and for your peace of mind.