You have tried everything but the obvious--fruit (though you did mention you had tried some fruit). Fruit is the only natural food for humans. I would make him fresh OJ and see what happens. If you want to take it a step further, all food that we eat kills us slowly, so it's easy to see why he is reacting that way. I hope MH has the time to respond to this because he has the healthiest happiest kids ever. I think they are raised on fruits nuts and berries, along with his herbs. I would not force him to eat anything, anybody can live well on juices. When he is ready to eat solids he will.
And about the parasites. What the MD considers "normal" is not acceptable. We all have parasites! All kinds of them! What you saw in his stool is parasites. You should try some parasite herbs. It is easy to keep parasites under control with a fruit diet.
Good luck, I understand your frustration but sometimes the best medicine is NOTHING.