Well the arm/hand/fingers could be some sort of RSI (from weightlifting and or /repetitive / desk work / lot of phone holding/crook of shoulder/neck? ) or sounds a bit like thoracic outlet syndrome, but the rest of the body is rarely affected unless you had TOS for a very long time.
*forward head/forward or hunched shoulders??
http://neurotalk.psychcentral.com/album.php?albumid=422

TOS useful sticky thread for info on that condition-
http://neurotalk.psychcentral.com/thread84.html

* sticky fascia /myofascial syndrome can eventually spread body wise as it the stuff that holds and wraps the inner body *

I don't knwo if it is all a single condition , or a combination, after reading more about TOS you might be able to tell if it might be a fit or not...
Many drs do not fully know about TOS, so if you think it might fit, find a TOS specialist..

If the magnesium you are using is the OXIDE form, it will not work for you. The oxide does not dissolve (ionize) in water, so remains in the GI tract never to get to the muscles and other tissues at all.

This is my magnesium information:

http://neurotalk.psychcentral.com/thread1138.html

You also need to know your B12 actual testing results. This is because labs report low levels as "normal". If you are below 400pg/ml...you are low and that leads to nerve damage.

I'm no doctor but I do know a lot about ALS and I can say that ALS has a very 'classic' pattern that shows on EMG and for it to be ALS all of the pieces of the puzzle have to be there. Muscle twitching can be anything or nothing and is most likely nothing when it's all over your body. People with ALS twitch in the place they have weakness AFTER a muscle fiber goes limp and becomes useless. Twitching in ALS is the distress signal of muscles that have lost their connection to their motor neurons. So if you can flex a muscle that is twitching then that 100% means it's not ALS. Benign Fasciculation Syndrom or BFS is a long term disorder. A lot of people don't know that BFS often stays with you for a long time before stopping even years. What you have is most likely a combination of things and not ONE thing. Maybe is CFS? Also it's common to have light atrophy in a hand/arm affected by Carpal Tunnel.