A little more info would be helpful, but the end result is probably a vet visit and change in husbandry somewhere. But, what is a while? Are we talking 2 weeks or months? Is he in shed, and what are the cage temps/style/room temp., etc? If it is a respiratory infection, meds will help, but if you don't correct the cause, it will probably just repeat itself, so might as well cover all the basics.