Hi
Since you are having pain in your left arm , there are only 2 possibilities at your age.
1.
Cervical Spondylosis with myelopathy
2.
Periarthritis shoulder.
Now , do you have pain and numbess in your full arm till the fingers and are you able to life your arm above your head and bring them back ? Definitely it is not due to
stress. Please do get back to me with your complete complaints.
Take care