Patricia, sorry you've had to have another go round of disappointment. I know exactly how you feel, kind of abandoned by the doctors, which is a bad feeling, considering that they are the ones who are supposed to figure out what is wrong with us and then fix it.
Speaking of Mestinon, I've never found that it affected my mood in any way at all. I do get 'brain fog', but that seems to be a product of the MG rather than the Mestinon. I would think the pred is the more likely culprit to be messing up your mind.
Hope things improve for you.
Hugs,