My most dear, most kind, most precious wish-fulfilling Tracy,
I read your emails, I am sorry for the long delay in replying. So the main thing for your son is to have very strong refuge in Buddha, Dharma, and Sangha, and then to recite the mantra of Black Garuda. The Buddha manifests in the aspect of Black Garuda in order to prevent harm from nagas and other beings, and to prevent disease for us sentient beings, specifically disease caused by nagas.
Your son should also take jung-nga and gur-gum [Tibetan medicine] when the problem arises. He should take it two or three times a day. He should also receive ga-gön puja. He has to be present for that puja, so he can make a request to a lama or geshe he has connection with, or to a meditator.
So please try these things for him. I am also doing prayers for him. Please live your life with the thought of bodhicitta day and night. This is the best life.
With much love and prayers...