I assume that, with the diagnosis of ADD, your son is receiving Aderall, Ritalin, or a similar drug. Many of the symptoms he “exhibits” may be attributable to the adverse side effects of these drugs, especially the “low appetite” and “lack of weight gain”. There are, however, other causes of failure to gain weight, some serious and many treatable and, if not already considered, his doctor should order whatever tests might be appropriate to rule/out physical disease, especially diabetes mellitus and hyperthyroidism. These drugs also have CNS side effects including insomnia, nervousnessnes and overstimulation.
Advair is, as you know, a combination of flovent (fluticasone) and serevent (salmeterol), the latter in a class of drugs called (long-acting) beta-agonists. Serevent is associated with a number of adverse reactions including hyperglycemia.
Thus, both serevent and flovent can result in hyperglycemia (elevated blood sugars, the defining feature of Diabetes Mellitus) and this can cause wt. loss or failure to gain weight.
The bottom line, here, is that your son’s signs and symptoms may be secondary to the drugs he has been using, to an occult physical problem (for example diabetes) or a combination of the two and these possibilities would best be addressed by his physicians.
It is very unlikely that food allergies or vitamin deficiencies are a part of his problems but, the information that you have provided does suggest a degree of malnutrition and this, in turn, would prompt consideration of some type of gastrointestinal disease, characterized by malabsorption.
And, finally, yes your son could be experiencing “emotional side effects” from any of the three drugs he has been using, either singly or in combination. For this reason and those listed above, it would be wise to look to the side effects associated with each of the drugs and this could involve exclusion, from his current medical regimen, of one drug at a time, under your and his doctor’s close supervision.
Good luck