I think I'm familiar with your problem have you considered that the recurrence is simply because of the houses your son may visit, the houses of friends, or family friends? Because the people may be infected maybe from your son or perhaps they gave it to him, if your son was cured but they were not perhaps each time he visits he can be reinfected. If you really care about your son I would consider that one, many, or even all of his friends, the places he has visited, they are all infected, maybe because of him, family friends, whoever, if he is in that much pain I would confront all the people he interacts with and tell them they may have pinworm infection. I believe the people he associates with are the cause of this recurrence, it could be just one person, but isn't that all it would take? If you tell them to get checked for pinworm and they discover they have it and are then treated successfully in that instance the problem may be resolved but if your son is being reinfected over and over and even after telling someone they have pinworm they do not get treatment you should simply keep your son away from those people or that person. As a last resort you could not allow him to visit his friends or anywhere he has been Because those places may be the cause of his recurrence. Thankfully he still would have the option of going outside and wouldn't have to stay in his house all day which could lead to him being isolated and depressed. It sounds like he's in a lot of pain and I believe the people and places he associates with are the true cause of this recurrence.