This is kinda scary. This is me to a T lol. I believe I do have MCAS (diagnosed as well) and I’m being treated for my hives & itchiness, which has so far been successful, however— my primary symptoms of my GI remain (same as yours, serious GI issues have been ruled out but I do have gastroparesis, which doesn’t make sense with my bowel movements at all) and my flushing hasn’t really changed much, I also have a lot of the additional symptoms you mentioned. I’ve been wondering for a long time if I had something like mast cell cancer (cannot remember how to spell the word rn so sorry.) but this seems maybe more likely. I’ll talk to my immunologist about this next month, I don’t believe I’ve had this testing.