I agree with Mr Smith, go and see a doctor.
In some cases when limbs are set in a cast, the muscle within that area does little to no work. When the cast is removed you can sometimes experience pain and this can sometimes be that your muscle has deteriorated slightly. As for the cracking, it doesn't sound good, but once again I'd emphasise on seeking medical advice from a doctor.
[This message has been edited by Chanters (edited 03-21-2005).]