I Am A 57 Year Old Female In Relatively Good

I am a 57 year old female in relatively good health; I take blood pressure medicine. Lately, my left arm has been going kinda numb on me; does not appear to be any particular reason why. Now the discomfort is staying more in my lower shoulder near the back. It comes a goes. I type all day at a desk -- but otherwise, can't figure out why this occurs.