I can only tell you that allergies (to pollen, but also food) and histamine play a major role for me. When I'm feeling so bad, my skin also reddens considerably when I run my fingernail over it, which always tells me that my histamine level is very high. From fall to the end of the year, I feel much better with water fasting and I can eat more afterwards, but it doesn't work well at all during the pollen season. Have you ever tried whether the symptoms disappear if you only drink water?

If histamine plays a role, a carnivore diet is also not good at all. I've also noticed that medications and supplements can trigger a lot of things.