Thank you for the query.
It looks like your son is suffering from partial bowel obstruction. And it seems he has been diagnosed but not treated. This condition is very probable due to abdominal adhesions
. As this can be partial only, there are times when stools flows freely and times when it gets blocked. Such blocked stool keeps accumulating and causes increased pressure what will sooner or later cause its passage. Such condition is very hard to visualize with tests. In my opinion, when no other explanation has been found, you should contact a surgeon and ask him about laparoscopy
Laparoscopy is a kind of surgery where the camera and tools are inserted into abdominal cavity through small holes. Laparoscopy will tell if there are any adhesions (probably there is a lot of them) and if so, surgeons will be able to remove this adhesions.
Hope this will help.