I don't have quite the same problem, but I have food allergies. If I eat too much wheat (gluten, actually), or dairy, then I feel pretty terrible. I break out with eczema on my hands, and the joints in my fingers get sore and stiff. But, if I stay away from those foods, then I'm fine. The eczema and stiff joints go away. My kids and husband have food allergies too, so we're quite the family, but at least we know what to stay away from.
I feel for you, eczema can be pretty terrible, sending hugs your way!