Mold is a dreadful word to a lot of homeowners. The first sign of a cold and some people think it is their home that is causing it. Having said that it very well could be an allergy to mold that is causing your sons issues.  First things first, only you know how characteristic this is of your sons’ health. If you think it is something in the environment of the home you should investigate. I personally would check for moisture first. I would start with the walls of his bedroom using the moisture meter and thermal camera, moving outward as necessary. I would also look at the furnace for combustion and venting issues. Lastly I would be able to take air quality sample and an outside sample to see if there are mold spores in the air that could be the reason for your sons problems.