Don't give up, cinusti! You are just running into something just about every one of us has experienced, the fact that MG is VERY dificult to diagnose, and that most neuros don't know much more than what they were taught in school about it, info which is quite often very out of date. There are neuro's who specialize in MG, but actually, if you are being referred to a neuro-ophtalmologist, that may be your best bet. They are sometimes the first to diagnose MG in someone who has mostly optical symptoms.
And as for the heat having caused more fatigue, if you DO have MG, that is exactly the symptom you would have expected. Check any web site with info on MG, and heat is always listed as one of the things that can make it worse.
Hugs,