Thanks for the additional info on the specific shoulder tests. I would have said before reading them that you likely have a RTC strain. And my best guess still holds after the additional tests.
Rest it. (No pressing until it is painfree)
Ice it.
Roll it. Get a tennis ball or lacrosse ball in a sock and roll the back of the shoulderblade against a wall.
When it is painfree, get a band and do isolated internal and external rotations. Work up to PNF diagonal patterns. And focus a lot of your workout program on lower trap strengthening.
