Medicine is not an exact science, but is a very logical science. Lab tests should be interpreted in the context of the clinical presentation. Abnormal test results may be a variant of the normal (by definition 5% of the population will be out of range for any given test) and by the same token normal test results do not exclude a clinical diagnosis.
One of my (excellent) teachers years ago, told me (when I was very puzzled by the lab results of a patient)-why do you expect a malignant cell to know which proteins it has to express on its cell surface?
You need a good physician who will meticulously take a full history, examine you, go over all your test results, possibly order more tests and put it all together.
The information we can get on the internet is not always accurate or comprehensive enough, but with that being said, much of what you describe (sadly, including the indecisiveness of your neurologists in the face of severe/life threatening symptoms fits MuSK MG).
The commonly used antibody tests may not be sensitive enough to detect all patients. Other tests are not yet commercially available but possibly those could be ordered by your clinicians.
You also have to find the way to better live with your illness,
Take into account that a diagnosis does not necessarily mean cure or even remission.
It is only a tool for your physician to better direct the management of your illness.
Part of MG management, in my opinion, is adequate supportive care. You can receive that with or without a definite diagnosis.