In an earlier post I suggested comprehensive stool tests. After considering your child's symptoms again, the problem may not be parasites at all.
There is another forum which may be more helpful to you. Try reposting in the "Candida and Gut Dysbiosis" forum. I'm not saying your child has candida, but he does seem to have a gut dysbiosis.
I feel certain you would get more help from this group of posters.