[Crowbob]

Try the 'beer can test'. Raise arm to level (horizontal) pretend you're pouring from a beer can.

Sharp, very localized pain?

If so, probable rotator cuff tear. If also weakness against resistance to downward pressure with thumb pointing down more like supraspinatus tendinitis/impingement syndrome.

Overhand smashes and repetitive serves can do it and show up years later. Rest (i.e, stop doing what hurts) and anti-inflamatories are your first defense.

Or see a doctor.