James, let me tell you from experience that rest and a proper course of physio is the best plan of action. I know that I would still be in pain if I hadn't stopped shooting and seen my physio once a week, plus doing my homework exercises with the stretchy band (which my physio has increased slowly when she sees it has become too easy).
I also suffered from a trapezius muscle injury a few years ago, which comes back to haunt me every so often. At least having been to the physio for that, I know what to do if I feel it coming on.
I just bought the book Archery Anatomy and have realised what the impact of shooting is on one's shoulders, especially (I believe the shoulder blades are attached by muscles to the shoulders, back and neck, so not just controlled by the back muscles).
I'm right handed and because I dislocated my right shoulder, my rheumotologist said I should shoot left handed. Of course, this works well for me because of my eye dominance (something in that book saying eye dominance is far more important than handedness, but that's another thread). So now both of my shoulders have suffered problems and it's only something a physio can sort out properly. If need be, I may have to have a cortisone jab to reduce the inflammation further.
I could tell at SoCo2 that my should was still sore trying to pull my regular 30#. I will need to wind down to 28 until I gain my strength back. I know you're desperate to shoot again, James, be get properly diagnosed. The trouble could be worse than you think. The longer you go without treatment, you could be damaging your shoulder.
For you own peace of mind and health, get thee to a physio!