I've noticed that my son is quite thin compared to other kids his age.
He has not gained much if any weight for quite some time now, although
he is growing taller. I wonder if it is because of the yeast/bacteria
in his gut and he cannot absorb the nutrients or because he is not
breaking down the food properly (although we give him enzymes to help
with that), or if it's because of metals or what?

I'm starting to get pretty worried about it. He actually eats quite a
bit and healthy food and chews and swallows no problem but he's just
not gaining weight. I wonder if they are going to make us do a scope or
something...