my kitten was really good about using his litterbox the past few weeks. but all of a sudden he won't use it anymore. it seems like he just goes where ever he pleases. i don't know what's wrong. to be extra careful we placed a litterbox in every room but he just won't use it. we haven't changed litter or anything, everything is the same. please help. it's getting to be a bit frustrating having to clean up after him every day.