Good Morning
Just reading your post here, sorry to hear how your son suffers because I know from my sons experience(10) it is not pleasant, for my son it is always 24-48 hours after eating, I always have to go back that far, it starts with nausea dizziness weakness hands legs pain all over headaches brain fog ravenous for food blowing hot and cold fatigue constipation it really is very debilitating and we are very strict with his food. These symptoms can last up to a week.
I do believe that coeliac is just not that straight forward even when you come off the gluten as there may also be other underlying or associated side effects but also accidental glutening despite doing your best…..