Just had shoulder surgery last month and having double knee surgery all from tendon issues. If it truly is tendinitis, then rest it and let the inflammation settle down. If it progresses like mine did into tendonosis, then the tendons are micro-tearing and you need to either remodel them through eccentric loading, use biológics like PRP or stem cell, or get surgery to debride and clean up the tissue. I tied everything.
An X-ray would show bone vs soft tissue so I imagine some of it is showing inflammation and arthritis of the shoulder. MRIs show the ligaments and tendons which might be worth getting.
I’m 5 weeks into not working out at all and have another month of PT. You pay now or pay later with this stuff. After 25 years of lifting I’m paying for it now.
Rest up, get some deep tissue massage and try to avoid repetitive movement that will irritate the shoulder more.