I suggest an orthopedic doctor or surgeon. The problem may be rather simple compared to the intense pain. Coincidentally I got my shoulder cortisone injection this AM. It took 10 minutes. In and out.
Pain since Oct 2018. I have a bone spur in the neck. Pinched nerve pain from neck to left arm. Forearm tingles and it feels like someone has a tight grip on the arm. Pain under the shoulder blade.
80% less pain now due to exercise like stretching, chin tuck, raising arms straight over head. Do this in bed and it really works. Use this memory form pillow (Slim Sleeper 2.7” thick.
Ibuprofen 200mg x 4 and twice a day.
Turmeric with black pepper.
I use a Ten device for electronic massage. It really works. Slap the pads on either side of the spine and bring the intensity up half way. Very long lasting battery. I ran it once last week for 4/hrs and the battery hardly drained.
Easy Home Pro EHE012PRO
https://www.amazon.com/Easy-Home-Professional-Electronic-EHE012PRO/dp/B01MXSPBUW/ref=sr_1_1_s_it?s=hpc&ie=UTF8&qid=1547236467&sr=1-1&keywords=easy+home+ehe012pro
cortisone is one thing. but if your rotor cuff is torn - as seen by an MRI - then surgery is the only real option. Tears do not just heal, they get worse.
Orthopedic/sports medicine doctors are not always reliable in their diagnosis. See an orthopedic surgeon. - preferably one with good referrals. Ask around for others who have had similar surgery, about their experience, and their doctor.
Always get a second opinion - preferably from a different hospital group/chain.