Right now, notice where your head is in space. Is it out forward over your chest, or is it more directly up and over your shoulders?
If not,then,as if someone pulled a thread from the top of your skullcap straight up...pullyour head up-
-and put your head back direct over your shoulders.
Doing this a little each day will loosen your back muscles & arm muscles a bit. (might even help with pain)
I bet you're nearsighted & put your head down to the screen when you read, just like me.