Concern for Buzz

https://imgur.com/a/GDSzHM4

Hello, I am a college nursing student and I live with my cat, Buzz. He is the sweetest orange cat that’s had some concerning changes recently. Buzz is y’all the type of cat that is eating the food that comes out of the feeder before it is even done dispensing. He is not underweight, he’s just been a big back since he was a kitten. If I open the fridge, Buzz pokes his head in and meows. He loves food. For the past month or so, I give Buzz a spoonful of wet food every other day. This is his favorite meal and he’s eating out of the spoon before I can even get it in the bowl. 3 das ago, I have him a spoonful of a new flavor of wet food, Friskies turkey in gravy. Every other can of wet food that he has had was this same brand, but never this flavor. Since then, he has had 2 episodes of diarrhea, which he has never had before. He has also barely touched his normal dry food that he has had for months. He is much less talkative than normal, especially when I open the fridge and doesn’t sleep throughout the night with me. I’m hoping he just has a belly ache from the new flavor, but was hoping for some other perspective. Being a college student, I don’t have much money, but if I have to take him to the vet, I would be willing to sell some things to help him as he is my whole heart. I included a link to some pics of him to enjoy :)