Sorry it went so bad
Was this a neurologist? Is he familiar with MG?

Well, maybe it's a good thing to see an eye doctor. Sometimes if we/they (patients and docs alike) focus to much on one thing, there isn't much room for anything else.
If this doctor sees something he/she recognises as MG, you can take that back to your neurologist. Or a new neurologist if that is a possibility.

One thing I do believe in though, is that if a patient has problems that have a significant effect on daily life, it's up to the docs to find out what the cause is.

I do not know if Mestinon working is only possible if you have MG.

It's hard if you're seronegative that's for sure (I don't know if you are of course)

Just to let you know, I did not have any ptotis the first years of my disease and I am sero positive for multiple antibodies. My ptosis only started after a severe exacerbation.

Hope the vitamin D helps.