Would echo the sentiments already expressed and do feel a check up at the vets for a UTI may be a good idea.

Try a second tray and some Cat Attract litter. Does he go out at all? Do keep trying different litters. A kitten we bred went to his new home and was fine for a day or two, using his tray, but then started weeing and poohing on the owners bed. I suggested changing the litter to the one we had been using. She did change it a couple of times but to other different types but this inappropriate toileting persisted - eventually when she finally got around to changing to the brand we had used he immediately stopped - and has been great ever since. You just have to figure out what he is trying to tell you!

If he is an indoor cat and you obviously have a lot going on yourself perhaps he is bored and is attention seeking so to speak. Would invest in a couple of Feliway plug-in diffusers, rotate his toys and perhaps put some Bach's Rescue Remedy in his water.

Good luck.

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Kaz

For kittens, joy is for the asking and smiles are for the giving