you have only mentioned pain in shoulder for years ,any associated stiffness
or limited range of motion,having DM? this long standing pain may be due to frozen shoulder
. it wax and wane over time.mainstay of treatment is analgesic
, intra articular steriod injection and last but not the least regular physical therapy
(streching excercise). surgery may be indicated in refractory cases. consult a doctor nearby.