This may sound strange - but I saw a Mystery Diagnosis episode not too long ago that described many of the same digestive symptoms you outlined.

Turns out it was a rare disorder (I think genetic) that kept the digestive tract from moving food through his colon. He could not execute bowels movements efficiently cause the nerves ending in the colon never triggered proper peristalsis responses. It got worse - and frequently intervention (ER trips) were necessary because the situation caused blockages. Once cleaned out - he'd be better for a awhile - but the inefficient bowel eventually blocked again.

I am so sorry I can not remember the name of the disorder! It is rare - and a gastroenterologist was one who finally tested for and dx'd it. I'll poke around the internet and see if I can come up with the name of the disorder they featured. I do know that it was in no way related to MG.

Sue