I'm putting my faith in the idea that reducing "leaky gut" is the key, along with eliminating allergens like dairy. I was doing pretty well all these years mostly avoiding coffee, dairy, and other things that increase leaky gut like MCT oil. My worst symptoms happened recently as I did all these things. The diet I'm on is meat-based, or, more illustratively, fiber-free. From my understanding fiber can often be actually harmful for leaky gut.

I've avoided mentioning this too much in the comments because I didn't want to seem to be advertising this, although for full transparency, I feel that I must. It's just what I feel is the best best... I've also started (very) high-dose vitamin D, so-called "Coimbra protocol", which really needs doctor supervision which I don't currently have but will promptly.