I am dealing with the same thing right now.
I passed 3 neuro exams (one by the top ALS specialist in Dallas who runs the ALS clinic sponsored by the Muscular Dystrophy Association- he is REALLY smart!)
I have had 4 mri's -1 brain, 1 neck, 2 spinal - all normal
My EMG of both legs and 1 arm was normal
Nerve Conductive Study all over body was normal
EEG (brain wave test) was normal
Yet I still have the feeling of perceived weakness in legs, off balance when I walk, twitching in calves, legs, back, thumb, buzzing on bottom of feet, cramping in my foot arch, etc. etc.
Its so hard to believe its anxiety, but that is what it seems to be in my case. Best advice I have to try and remind yourself that the doctors are taking you seriously and looking for something clinical to diagnose you with - makes them more money anyway to keep you on as a patient requiring care. If they are telling you to go away and that you are healthy you have to try and believe them. Its something I battle with daily.