If you have MG, a neuro-ophthalmologist should be able to fatigue your eyes and determine if you have it. They do very specific visual tests to look for double vision as well. JUST GO SEE ONE!
Has your neurologist done MIP and MEP? If not, they need to do that.
I can hold my breath. Not as long as other people, but I can still do it. That IS NOT a sign that you don't have MG. I don't care how good your doctor is, he is not a neurologist. Their job is to assess your breathing and look for any patterns, such as restrictive or obstructive, and to see if there are any signs of neuromuscular fatigability (via MIP and MEP).
You might not have MG, but someone (or a group of them) needs to figure out what it IS, not what it ISN'T!!
Annie