Myasthenia Gravis Support Group
Myasthenia gravis (MG) is a neuromuscular disease leading to fluctuating muscle weakness and fatiguability. The hallmark of myasthenia gravis is muscle weakness that increases during periods of activity and improves after periods of rest. Although myasthenia gravis may affect any voluntary muscle, muscles that control eye and eyelid movement, facial expression, and...

When prednisone started working for me after several months of taking it, Mestinon actually made me worse rather than better, as I didn't need it, and only got the side effects. So you might try not taking it for a day and see if that makes a difference. I got all sorts of cramps from it and actually was quite happy to get off of it, even though it meant taking more prednisone.
Mestinon is very short duration acting, and very quick to work (minutes and hours) so if you skip taking a pill you can take one and 1/2 hour later it will take effect.
Hope things smooth out for you. Persist with pushing your neuro to find solutions as when they don't hear from you they assume you are OK.