There are many tests that a doctor can perform such as the adrenal, thyroid, even melatonin, hypochlorhydria etc. I am sure they are pretty accurate. I am surprised to hear that your thyroid test was negative. Just curious, Do you have the figures?
Also my son suffers from a few things and I know that it is due to nutritional imbalance. Sometimes it takes a while for children to accept the facts. Hang in there.