It sucks to give them up, and while this is not really a "substitute" for potatoes, I have discovered that I really enjoy sweet potatoes. They don't taste much like regular ol' spuds, but they're a good sub in some dishes.
I think I might have a lectin intolerance...looking into that next.
I think for most of us, we've had to do the detective work on our own. Doctors just want to diagnose what they recognize, and if it's too hard to figure out, they pin a label on it that makes no sense. My philosophy is to listen to your body, it knows what it can and can't handle better than any doctor.