He's having poopy problems.
I'm guessing he ate something that disagreed with him yesterday.. his poop is runny and he's squatting every few minutes when he's outside. Inside, he sulks, because he hates having the feeling of poop on him. :P (he sulks whenever he has poop stuck to his bum).
I'm not worried about him yet, he's had similar happen before and it goes away quickly. I've checked the entire area around his bum and nothing is obstructing. I'll be keeping en eye on him. I'm just amused and empathetic because he's been sulking all morning. My poor boy.