I'm sorry this is so discouraging for you. I know how frustrating it is when you're trying so hard to stick to a healthy diet and you still hit setbacks. Have you ever heard of Cyrex labs? They do a lot of different tests for food sensitivities and gut permeability and I'd really highly recommend getting some tests done. I was in the same boat as your husband last year. I had been gluten-free for a year but still felt like crap, in fact I felt even worse than I did before going off of gluten. Constant digestive issues, extreme fatigue, hormonal problems, you name it. I got a few Cyrex tests done and I found out that being gluten-free wasn't cutting it. I'm also sensitive to dairy, corn, amaranth, teff, and tapioca. I was SO overwhelmed by this, but I actually felt better after going off of those foods, so it was worth it.
I think that sometimes you can go on an elimination diet where you cut out all foods that can cause sensitivities such as grains, dairy, eggs, nightshade vegetables, etc., and then add them in one by one to see if you have a reaction. To me, it was worth it just to get the lab work done, but you might want to think about that as well.
Gut healing is a weird thing because it really does seem to get worse before it gets better. Hang in there.
I also found success with the food intolerance blood test. Mine was a different company. As soon as I eliminated those foods, my inflammation calmed and I could raise my arms above my head (literally was in too much pain previously). I still struggle with my health but quelling the constant inflammation has allowed my gut to heal.