if he is licking his bum alot it could very well be his anal glands. Does he scoot across the floor on his bum??? Also it could be tape worms? Check his stools or around the rectum for evidence of this. If he is licking his wee it could be uti or bladder infection as well as kidney problem. Have your vet take a look at him for these problems.
If the things that everybody else suggested are ruled out, maybe it could be boredom. A kong or a rawhide bone or something else that he can chew on that will occupy a good deal of time might keep him busy doing something other than licking himself.
"Be who you are and say what you feel. Because those that matter, don't mind...And those that mind....don't matter."