I think it's important to remember eating equals pain for your son, so it's little wonder he doesn't want to eat. I would really look seriously at the GAPs diet, because it is nourishing without all the possible allergens.
I have never heard of this, but will google it now. To be honest any diet would be an improvement. This is a list of what he eats and even then its not that much.
- dry cerial
- soy milk
- dry gluten, egg, nut and dairy free biscuits
- choc oreas
- maybe a sandwich (white bread) he wont eat gluten free bread with choc mud (not free alternative to nutella)
- 2 min noodles
- lollies
Weekends are the worst as he eats barely anything. He goes to pre-school 5 days a week mainly because he will at least eat something there, not a cooked meal like the others, but some noodles or some sanwich.

He does not eat dinner at all!
Will look at this GAP diet and hope the peadi and dietition have some answers!