I was diagnosed 10 days ago with primarily occular MG although I have some involvement of my face and neck. I have probably had it for a year and a half before reaching this diagnosis. The eyelids aren't bad but eye movements (and chewing, talking) fatigue easily, especially towards the end of the day. I am still waiting for the results of antibody levels and so forth.
Mestinon helped me within the first 15 minutes of taking 1/4 of a tablet. I don't know if I am just lucky, but the neurologist thought that the positive response was pretty strong evidence that I had MG.
I am still in the learning phase of this problem as I am sure you are. There is a lot of variability between sufferers of MG and my own symptoms have varied over time. There are a lot of knowledgable people on this site who have a lot of experience. There is also a list of helpful links.