Try releasing the the muscle tissue first. any tendonitis is over use of tendons. For exercises internal/ external rotations with a light resistance band when comfortable move up to a heavier resistance. focus on certain stretches to eleviate the tension. i would focus on tissue work with a combination of ART, gua sha (graston), cold laser, and kinesio tape. if pain is mild i would suggest more soft tissue first unless you can recall a lifted that aggravated that region. Like studhammer mentioned see an ortho for further assessment. I typically say go for the least cost effected by using soft tissue treatment and if pain is severe then get an ortho involved. also try strengthening upper back trap,scapula, lat and rear delt.