How long has it been going on?

Have you started a new job?
Has your job changed hours?
Is there a new friend?
Are you around the house less?
Was there another pet that was his friend that is no longer there?
Did you just get him declawed??
Did you change to a strongly scented litter?
Did you go from an uncovered to a covered litter box (again, smell)??

Trying to think of what would affect the emotions, what I've experienced with my own cats as well. Sounds like he's sticking to soft surfaces (unless your whole place is carpeted). Is he sore in that rear area?? Are his pawpads sore??