Hi Incata!
Sounds like you've had a rough go of it.
My son's allergist always said that he doesn't treat test results, he treats people - which was his way of saying that tests may be helpful, but they are not perfect, and should only be used
along with a clinical history. For example, when he was younger, my DS tested negative to milk, but clearly reacted. So his allergist considered him to be allergic to milk (outgrown, fortunately). He also tested positive to things he had been eating with no problems, so he said to ignore those tests.
Hives are not always present during anaphylaxis, contrary to what many people think. And that can make it hard to convince others that you are having a reaction. My DS also didn't hive up from milk, but flushed like you describe.
I don't have an answer to why you don't react to skin pricks or blood tests, and I'm so sorry that you have having a hard time finding competent medical care. I hope you can find someone to give you answers, and in the meantime perhaps consider getting a MedicAlert bracelet.
Best of luck to you!