Dear R When you had your MRI was it ordered with MS protocol? That means nothing less than a 1.5 T machine, using contrast and slices no more than 3mm in width on brain and spine..if not, make sure they rule out MS with proper protocol. I have had similar signs and symptoms to you as well as other muscular fatigue and twitches, visual probs and walking etc and I thought that MS was ruled out, which they said it was in the begining but I found a site on google after asking "Can you have MS with a negative MRI scan"? five pages of very interesting reading, Dont take their word for it, investigate, this is YOUR LIFE,  I just wish I could find a Dr that is as passionate about my life as I am. I am a single mother with four children and their father is living with ALS, and I have no answers on my own problems of the past 6 months, Good Luck, Kindest Regards Tracey