Rotator cuff tears are uncommon in someone as young as you but the classic symptoms for a tear are weakness and pain at night in the affected shoulder. When you are a 20-year-old pitcher or quarterback it usually takes a significant trauma to injure the rotator cuff tendon.
As we get older, many times the rotator cuff tendon can tear without trauma on a gradual basis. Not all rotator cuff tears require surgery to fix them but I do recommend you see an orthopedic surgeon for evaluation of your shoulder.
In addition to the physical exam, X-rays will likely be taken to make certain there is no calcification of the rotator cuff tendon or bursa, arthritic narrowing, or bony spurs. An MRI scan may also be necessary to assess the condition of the tendon. It is also important that you maintain your range of motion so you do not get a secondary frozen shoulder with scar tissue that can form.