I see this as a double choice question:

A. surgical eye problem
B. generalized MG

You forgot :

C. ocular MuSK MG, worsening with mestinon.

My suggestion: try to gradually decrease the dose of mestinon (never do things abruptly when you possibly have MG) and see if you are any better.

20 years ago, I was hospitalized by a neurology resident for an MG exacerbation. (A few months earlier he prescribed mestinon for very mild symptoms I had). I gradually took more, because I wanted to have a normal functional level. The leading MG expert who saw me the next day, doubted this diagnosis (because all my tests were completely normal), so all my medications were stopped. A few days of bed rest in the hospital and stopping mestinon led to complete resolution of all my symptoms. This clearly ruled out the possibility of MG. I was told that I could keep on taking a very low dose of mestinon and actually advised to stop it all together (which I eventually did). I had no MG symptoms for 15 years.

In retrospect, I had very mild MuSK MG then. The mestinon made it worse (even though it sometimes led to improvement which confused me and made me think I should take more). Once I stopped mestinon, I could easily adjust to the very mild symptoms I had (or possibly they indeed totally resolved) and lead a completely normal life.