Yeah, it's pretty complicated. I have gotten blood, stool, and urine tests and all have come out fine. Food that previously would never cause any issues cause massive problems nowadays. Did your issues come from any dietary changes? How did they appear?
Yeah, I ended up abandoning veganism, because I no longer felt (and feel) the empathy that I did back in the day (if there's much left). Being able to experience the world through the lenses of someone with low empathy makes you a little sympathetic (heh) to those that are born like that. Basically my decisions are purely rational as of today. I'm lucky to not be impulsive at all; if I were, I would have fewer friends than I do.
I briefly answered the dietary changes in another comment.
It's hard to say. The diet was vegan, but it was a poorly implemented vegan diet. I was basically eating a lot of fruit and legumes, far too much fruit I should say. Once I started having the digestive issues, I started reading about it on the Internet, and I came across some sites talking about copper overload, how vegan diets inevitably suffer from an inbalance between zinc and copper, but I'm not sure if it's pseudoscience or not. I do have low ceruloplasmin, which is the molecule that carries copper around the blood, so that is at least interesting, but yeah, could be coincidence. In any case, I haven't managed to fix it unfortunately, even after switching to an ordinary diet.
About five years ago, after experimenting with some diet changes, I started having some pretty terrible digestive issues, like extremely bloating and indigestion. The issues would fluctuate, sometimes being much worse than others. Along with it came personality changes, like apathy, and they would also fluctuate along with the digestive issues. It's actually pretty scary how much it affected my brain. There are times when the apathy is so extreme I feel like a psychopath, and that comes from someone that once upon a time was vegan due to ethical reasons, so I am (or was) an empathic person. It really is mindblowing. The thoughts I have had and sometimes have would put me in a psychiatric hospital, thoughts I would have never imagined I would have.
The exact same case for me.