You might want to start by reading this thread: https://www.healingwell.com/community/default.aspx?f=32&m=457357
which will begin to answer your questions about the diagnosis process and what a doctor looks for, to make such a diagnosis.
Yes, it can take a very long time, sometimes, to get a diagnosis, as there are lots of disorders, some of them neurological (like MS), others metabolic (like diabetes, thyroid problems,) that look alike from the outside, and which can affect you in many of the same ways.
Apparently you've had some testing done already at a neurologists office? Why don't you tell us what you've had done already, and maybe we can offer suggestions about what else you might consider.