I was very active in 2013 (age 47) when MG hit me like a brick. Unfortunately, it would take another five years, six hospitals (including University of Chicago, and Mayo), and countless tests and retests before I wound up hospitalized due to shortness of breath. That was when someone finally realized my diaphragm wasn't able to move air properly and I was given a Mestinon trial for reasons I didn't yet understand. Within a week I no longer required a cane for mobility, or need to sleep upright because I couldn't breathe lying down. The successful Mestinon trial confirmed Seronegative MG in December of 2018.
My own research had indicated MG early on but I couldn't get anyone to take me seriously and was even referred for cognitive behavioral therapy by one neurologist because he believed it was all in my head.
On a side note, my 85 year old father just tested positive for Generalized MG after I witnessed him going through the same runaround as me after presenting very similar symptoms. My advice would be to not let your health concerns be easily dismissed, you know when something isn't right with your own body.