My throw hand middle finger used to get sore (joints, not skin), so I started throwing so that the string coming from my middle finger drapes over my index finger. Hard to describe, but I’ve seen some pros do it as well. It really reduces the strain on your middle finger by distributing the force of the throw through your entire hand rather than yanking on your poor middle finger joint all the time.
I don’t even think about it anymore - it feels pretty horrible (not painful - just unnecessarily strenuous) to throw without doing this.
As far as the shoulder goes, I would just say give it a week off, and then ease up on your throw a bit while incorporating my little tip for your finger - who knows, your finger pain and shoulder pain could be closely related. A lot literally hinges on your elbow, so your fingers, forearms, upper arm, and shoulders can all refer pain to each other in some odd ways.