About a year or so ago I ate some raw shiitake mushrooms as I was preparing a noodle soup, then I just cooked the rest lightly in the broth. 2-3 days later I was raw with striated lashes all over my legs, torso, back and a hideous itchy rash everywhere, yes everywhere! It was almost reaching my eyes, which can be dangerous and can impair vision. I went to A&E immediately as it started to crawl,up my arms from my fingers etc... They gave me steroids tablets to take and there is a topical antihistamine you can get in tablet form from Boots etc.. Which does work well to reduce the itch. Other ones do not have an effect because it is a reaction of the skin. It is a sit and wait it out situation. Mine lasted for 10 days which was unbearable! I have not eaten even a regular mushroom since! And I have not missed them either.
Good luck to all, I feel your pain!