There are a few possibilities and others have mentioned some of them. Has he had a vaccine in the last few weeks or months? That triggers new or returning symptoms in some. Have you moved or changed schools? That could indicate something in the new environment, such as mold. Any recent dental work? That can be a trigger for some. I agree with HopeinHIM - if he hasn't been evaluated by an LLMD for Lyme, Bart, etc, this would be a good time. These infections deplete the immune system and can cause allergies, immune deficiency and autoimmunity.