As a little tip I wouldnt necessarily practice just one chord over and over again. This is forcing your hand into a painful static position. I would recommend alternating between a C and a G chord. The G chord stretches your hand differently and should loosen the muscles up a bit more. Its still gonna hurt though :(

Something I found was useful was buying one of those hand excercise things (mines a "Gripmaster" haha) these are designed to build up the muscles in the hand (I think the gripmaster ones are distributed by D'ARRIO) I use this when I'm watching TV or at work or whatever and it makes a noticable difference in the muscle strength in your hand.

Hope that helps

Neal