Oh, poor honey! Both of you! I know exactly how frustrated you are bc I've been there. I would cut out all veggies and grains for now and go very simple. First are you feeding chicken? If yes, cut that out bc that could be the culprit in terms of meat.
If it were me, I'd give whitefish and mashed white potatoe and about a teaspoon+ of steamed/pureed green beans (greens will help alkalize the digestive tract). Nice and simple. Hypoallergenic. Pumpkin is great too to help firm up. The only fiber additive that's considered "safe" is Benefiber - just a pinch. But you could def. try the canned pumpkin first. Yogurt or a probiotic supplement may help re-balance his intestinal flora. I would keep him on a fish diet for at least a week, if not longer, and then reintroduce one meat at a time - and then one veg. at a time if you want to include veggie (though they're not needed).
Please keep us posted, I really feel for you bc I've been in your shoes!!
