Should not happen or should i say , it has never happened to me . Check your grip on the pick , if you are holding onto it too hard , that could cause the pain , you onlly need enough pressure to stop it slipping when you strum , The power chord is just the root note , the fifth and the higher octave of the root note , because there is no third , it is neither major or minor , Sort of misleading name and you really don/t need to strum it that hard , Good luck