Hope your PT appointment went well - have you been doing too much exercise?
Apparently my left rotator cuff doesn't appreciate all the planks, tripod push ups, and using weights I'd been doing so have a touch of tendinitis along with something called upper crossed syndrome from all the years of doing a desk job. Have to take a break from the yoga and anything that puts strain on the shoulder and get the shoulder muscles strengthened up. All part of the "it sucks to get old" category.