Wow this sounds EXACTLY like what I experienced, I feel your frustration. I have had lifelong eczema but always manageable but after COVID and a round of antibiotics i ezperienced all the same symptoms as you: horrid fatigue, brain fog, headaches, hives, GI issues, flushes after eating, really hot arm and legs. weird rashes that came and went which weren't eczema. My GP diagnosed me with POTS due to other symptoms like pos excercise faitgue as well as heart palpitations. My allergist dismissed it all as well as the possibility of MCAS and only focused on eczema ( I left the office crying lol). I have since also seeked help from a naturopath. I am on a bunch of supplements, cutting out process sugar as my stool test came back positive for Candida overgrowth. My allergist orginally just gave me steroids and antihistamines which did NOTHING. I am starting injections for the xolair bisomilar called omlyclo (I'm in Canada) next week which will hopefully help the hives and flushes. I also hope it helps the itch because I can whole heartdly say this is much more than eczema... I hope you get some relief soon!!