Sir my left shoulder pains while doing excercise in gym..

See orthopedic surgeon as rotator cuff tear is not a rare occurrence. Avoid heavy exertion until this is diagnosed and handled

You could have a rotator cuff injury, or impingement syndrome, or any number of orthopedic or musculoskeletal problems related to your exercise or anatomy. You should see an orthopedic surgeon to get the proper tests and treatment.