Why is my right shoulder always in pain after i finish playing tennis?

Rotator cuff: Likely etiology is irritation to your rotator cuff. The rotator cuff is a group of 4 muscles/ tendons that support the shoulder joint. Overhead or behind the back movements such as a tennis serve are classic mechanism of injury. Both inflammation and weakness are typical components and must be treated for complete resolution. Modification of activity is often required. Continued pain-tear?

Unstable Shoulder: Overhead sports like tennis require a high level of kinetic chain coordination and patients that don't naturally activate the entire core/kinetic chain can easily overload the shoulder. If you have been experiencing pain for a prolonged period as you mention you may benefit from an evaluation with a shoulder specialist.http://www.theshouldercenter.com/shoulderpain/2012/shoulder-specialist/improve.