How long should someone rest muscle due to high cpk elevation and what to do when it has been a month in a half?

Need diagnosis: High CPK indicates some degree of muscle cell damage or death, and is often an indicator of a muscle disease, (myositis or a muscular dystrophy or another type of necrotizing myopathy). It may also indicate rhabdomyolysis which has a variety of causes. Rest alone is not appropriate for any of these except, perhaps, rhabdomyolysis. So you need to consult your doctors as to the cause of your cpk.