Hey Polly, Welcome!
I agree with Suev that it's more of a profound sense of heaviness that I feel. Oftentimes, the heaviness is so bad that I can't move my tongue to touch my back teeth. My symptoms are very severe in the morning as well (Which is a bit unusual with MG). I also have shoulder weakness, chest weakness, finger weakness, tongue and palate weakness and arm weakness.
The symptoms in my hands are kinda odd, and I'm pretty sure that I have something else going on. I have a lot of stiffness as well. I also have finger drop after typing for a bit (the last three digits on each hand just drop downward). I also have constant twitching in two fingers on my left hand. My doc. doesn't think that these are caused by MG and as a matter of fact, I had an EMG done on my left arm and he found denervation (the nerve's not really meeting the muscle). This can be a feature of MG but is very unusual, apparently.
Anyway, the way that you describe the spasming and stiffness sorta reminds me of myotonia/spasticity a bit...Has the doc. ever mentioned this to you? When you say that you can't seperate your fingers, is this constant or after activity and then it resolves?
Anyway, I hope that you get some answers soon...The symptoms you're experiencing definately sound distressing...The fatiguability sounds like MG but the stiffness and such kinda sounds a bit like something else is going on..
I wish you luck and I hope that it all gets figured out soon!

Nicky