Til somebody smarter and with a better memory pops in......

Mestinon does NOT help unless you have MG. Some (really good) neuros will diagnose based on your response to this alone.

Mestinon ONLY lasts for 3 to 4 hours -- so your experience is spot on.

Yes, you can have MG with negative bloodwork and SFEMGs.

Uh, I don't know about prednisone. It is the "good/bad" drug. It can help you, BUT cause all sorts of other problems. Read a LOT before you make that decision.