I think there may be a point here about fretting the Guitar as well as finger or flatpick attack on the strings. When I used do a lot of tution I used work to stop students from placing their fingers tooo far away from the fret wire. That alone creates a lot of *unnecessary* tension in the left arm. The secret is to use a Gut strung guitar when you begin and graduate to the steel string after chords are learned.

Right hand problems are always about timing and bad posture, get compfortable, get a good teacher if the present one is making it a pain to learn. It is not that hard to learn

Finaly learn to listen correctly - if you cannot get it and you have a sound card and a wav recorder then record the bits you cannot figure out, slow them down twice or 200% then sing along with the result. It is realy very easy to play well and have fun as well, it need not be a pain.

I don't a thing about medicine but what Gargoyle posted makes a lot of sense to me.