Hi,
I'm sorry to hear you are struggling with your medical condition. It can't be easy, especially the constant itching. I am awaiting a bone marrow biopsy to confirm if l have systemic mastocytosis. I do have some of the symptoms you talk about. I try and keep to a low histamine diet, but sometimes this is not always possible. I have seen a dietician and she told me a low histamine diet is not a healthy option. So l tend to be careful what l eat, and try and avoid the foods high in histamine and sometimes, eat things that are lower in histamine.
I find yoga helps with my well being, as having a rare illness can sometimes be hard to deal with. I hope other people with systemic mastocytosis reply to your posting, so that you realise you are not alone. All the best.