I'm concerned that you're going from doctor to doctor, having the same tests repeated, and doing that in such a short period of time...
that unless you have significantly worsening of symptoms in between these visits, it may well be that all the tests will continue to come back "negative", or inconclusive, and you'll have spent a considerable amount of time and money to not get any answers.
Did your neuro dismiss you? That is, is he willing to continue to try to pay attention to any new symptoms that come along, or increasing intensity of current symptoms, or has he said something like, "I can't help you, go find help somewhere else" without giving any further direction (other than going to the Mayo clinic).
Did you say to him, "...well, then, if all the tests have come back negative, and I'm still experiencing these symptoms, what else might it be? Perhaps it is not neurological in nature; should I be seeing some other sort of specialist?"
There are so many different diseases that "look like" MS from the outside, doctors are indeed reluctant to diagnose unless they get some confirmation of symptoms through the tests, and apparently all your tests are coming back negative, right now....
I think if I were in your situation I'd go to one (or both) of the visits you already have scheduled, and then if there are STILL no answers, then pursue the Mayo clinic.