My cat has suffered a complete personality change
My cat was a stray my mom found near her work. He's around a year-and-a-half and we've had him for around eight months.
He used to be the most playful, affectionate cat you could find, almost dog-like. He'd come greet us when we came home, follow us everywhere (and push the bathroom door open if we closed it), do these little trilling sounds constantly, asking for pets, climbing on everything, running around like crazy... basically very active.
A few days ago, however, he completely changed. He's sill affectionate in the sense that he always wants to sleep close to me, but he never wants to play, he doesn't greet us anymore, is almost completely silent. He just wants to sleep all the time.
He was neutered around three months ago. At the time I worried he'd become like this but nothing about him changed.
My mom thinks the neutering is 'kicking in' now, but I think it's odd that it would happen so long after and so suddenly. He literally changed from one day to the next.
We also got a new kitten around a month ago. We worried he'd be jealous, but he loved the kitten. They were always playing together, wrestling and chasing each other. Now he ignores the kitten and even goes away if the kitten insists on playing too much.
He got a scratch in his eyes right before this change happened, we believe it happened while he was playing with the kitten. It got a bit swollen and pink, but it passed and now his eye seems perfectly fine, so I don't think it's that, but it happened right afterward so I don't know.
He doesn't seem sick. He's eating just as well as before. It's really just that he's so lazy and unresponsive compared to how he was before.
My mom has observed him limping a few times, but I haven't seen him do that at all. Any idea what could be happening with him?