Hi Penance. Wow. 51 years. You are the expert here. Have you been using Mestinon all that time? It is usually just a stop gap medication and it can become less effective with long term use. Are you also using an immunosuppressant like Azathioprine? If not, I'd ask my doctor about that.
My experience is that generic Mestinon worked wonders for me and I never used anything but the generic. But about eight months into an Azathioprine regimen I stopped taking Mestinon and now I don't need it at all.
Please note that Mestinon does nothing to reduce the amount of bad antibody in your blood. It just helps you cope. My preference is to reduce production on the antibody.