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...
From the web:
Inactivity or temporary paralysis of the muscle in the intestine prevents the passage of food through the intestine and can lead to a blockage in the gut. Pyridostigmine increases the nerve messages to the gut that make it contract and helps it move food along.
http://www.netdoctor.co.uk/aches-and-pains/medicines/mestinon.html#ixzz2Vom9SDlf
Good Luck
If dr. agrees you could try going off mestinon for five days. Then start it again and see what the effect is if any. My guess is it is something else that is causing the constipation.
You seem to have a good sense about foods and quite possibly they are causing reactions. I hope you can figure out the culprit.