From what I understand about MG and ALS:
MG fluctuates -- you are usually stronger in the morning and weaker later in the day -- you may be able to talk one day and not the next -- repeated use of a muscle makes it stop working, rest makes it usable again (for a while, at least).
ALS doesn't fluctuate -- once you lose a muscle, it doesn't come back.

My two cents -- your symptoms are CLASSIC MG. You may not be taking enough Mestinon -- or taking it often enough. Do NOT, however, increase your dosage without your doctor's approval -- overdosage is DANGEROUS!! There are other meds that can help with your stomach issues.

Prednisone can actually make you WORSE in the early stages -- you need to discuss this with your neuro. When you have Bulbar symptoms (talking, swallowing, breathing), you are supposed to be given steroids very, very carefully at first so that you will NOT go into crisis.

When you are stressed (worrying about whether or not you may have ALS), you will make your MG "misbehave" even more. MG does best when you take a "chill". Try to "go with the flow" as much as possible.

Learn from the people in this group -- they are AWESOME -- they KNOW their stuff!!!