In your case the problem may have been there for a long time, but repeated clicking of the
mouse or any such work (thus injuring the tendon of
index finger) could have triggered the pain now. Application of ice pack, anti-inflammatory drugs, wearing wrist braces, stretching and strengthening exercises when the pain subsides and modification of the way you click mouse or such work goes a long way in avoiding further injury and treating the present symptoms. Try these tips.