I'm right-handed...why can my left hand play piano so much faster?

My left hand can play very fast when it comes to repetitive parts, but my right hand won't. My left hand can roll the wrist and keep from getting tired... my right wrist appears to be frozen in place, and thus my right arm hurts. DOES ANYONE HAVE ANY TIPS FOR HELPING MY RIGHT HAND PLAY FASTER? I've been working on this one Mozart song for years. Seriously.