Lately I’ve been having pain in my rear/lateral left deltoid… pain came unexpectedly…no added volume or different workouts… pain occurs when I try to reach back, press over head or extend my left arm far out into my right side on the rear part of my Delt. Use to hurt a lot when incline pressing, but that has decreased a bunch where it’s doable to say the least. Any tips or suggestions as to what it might be or treat it? Thanks in advance!