dear Dennis,
May I ask you a few questions before I get to answering you properly.
How old/young are young?
Did anyone every tell you which nerve was damaged?
Do you have areas in your left arm that are numb?
what is your occupation? is playing the guitar a lot your job? your hobby?
What else do you do (work, physical activity)?
If you could tell me this I will react as soon as I can with some proper advice.
kind regards Esther