I'm not a doctor but I do have a suggestion based on my own experience.
After problems like that including breathing problems, and years of misdiagnoses since I was a child, I was finally food-allergy tested. It revealed allergies to peanuts, corn, soy, etc. Of course I had been eating all of those things for most of my life. My peanut allergy symptoms were like that of a flu; extreme weakness, breathing problems, muscle aches and pains, major listlessness, and so forth. I am also highly sensitive to MSG, which brought about a whole different series of symptoms. If your child hasn't yet been allergy tested, I would wholeheartedly recommend it as part of a work up.
Bunkster your question would be better answered on a pediatric forum.
JCH MD