I'm sure after 55 years you've tried everything. So I'm not sure my experience is relevant.
However, when I had hives 8 years ago, both my GP and the dermatologist I was referred to were unable to help. I was plagued by them. I had them all over the trunk of my body, on my arms and legs. Twice I had them on my face, including making my mouth swell up. They made wearing my work clothes so uncomfortable.
Eventually, I tracked it down through trial and error to be related to thrush, or a yeast infection (I did not feel that I had thrush in the usual way however). I bought several doses of the over-the-counter thrush one treatment pill and took two a day for a week.
The hives went, never to return.