Please help I think my chin is sick

About a week or two ago I took my chinchilla to the vet because I thought he was constipated they checked his poop they checked his teeth and they took his temperature and he said he was fine but they told us to change his hay and give him different pellets so I did my chinchilla didn’t really eat his pellets but he ate some hay after that he was fine But today I got him out of his cage he just sat there on my desk and pooped The poop look different than usual and he was kind of shaky and whenever I press on his stomach his teeth with chatter he and keeps breathing fast. My friend said it could be because of a sudden change in diet i’m not sure what to do please help I’m so worried