Explain how the problem came about for me. I've got labral tears in both my shoulders, and used to and still sort of do, suffer from weak rotator cuffs, so have to be careful when doing any rear deltoid work. Luckily they've healed fairly well and am able to train with minimal/no nuisance from them.
Sound like either a deep strain or a tear by the sounds of it feeling internal. Read up on the rotator cuff and how the humerus sits into the socket. Theres a small lip/ledge of muscle(i think) to help keep it in place as the socket doesn't encompass the head of the humerus. Good of you to rest it, takes a long time to heal as the shoulder joint isn't simple. Some light shoulder 'rehab' would be the best bet before you return to training properly.