I believe there are some medical problems that we don’t yet have the skill to diagnose.
I also belief that the mind and body are interlinked and stress etc can cause real physical symptoms.
I think you’ve reached a temporary end of road in your search for answers with the medical profession, if they won’t do further tests.
I also have unanswered medical problems (extreme fatigue and other symptoms) for most of my life and I’m probably much older than you.
I am currently living my life as best as I can and adapting my life style to fit in with my symptoms. I am being as healthy as I can be and managing my stress as best as I can.
I have accepted this is my life now. It may be that in the future some symptom may arise or some blood test will show something that will lead to a diagnosis.
I also believe that blood tests don’t always tell the whole story. Ie I read that the NHS range that show normal results for say, thyroid, are not the same in other counties. So a normal in the UK may be deemed too high, or too low in another country. I also think that some people are just more sensitive - so a normal reading at the low end could still cause problems for some people.
You don’t say how old you are. I found the menopause added a whole load of new symptoms, and many of your current problems sound similar.
I would suggest that you concentrate on dealing with your current problems and read widely to find any solutions. Ie I find cold gel packs really helpful for burning skin and hot sweats. I also seem unable to regulate my body temperature.
You may find something happens in the next couple of years, or you read something that helps to find a diagnosis- and may lead to further tests.
Someone suggested FND. There is a book called It’s All In Your Head which deals with this topic. But I actually think that even if they can’t find anything medically wrong with you - it doesn’t ALWAYS mean there is nothing medically wrong with you - but agree that the mind can produce real symptoms.
There is an article online about a guy who was practically bedridden and discovered through his own research a problem with his own adrenal glands that the medical establishment said wasn’t possible. He proved them wrong and is no longer bedridden and gives talks on his surgery and recovery.
Not having a diagnosis can be incredibly hard, so I understand why this matters. Not every medical problem has a cure or can be easily treated. The only consolation I can offer you is that after all these tests, you pretty much know what you don’t have. If that is in fact any comfort to you?
Just because you don’t have an answer now, doesn’t mean you will never have one. Just try to deal with what you have for the moment in the best way, and hope for the nearish future that things will change as medical knowledge increases.