Sorry ‘bout your tidder tat. We have had so many of the little guys over the years we are considered eccentric.
We learned a long time ago when the cats get sick, and the vets basically just take your money the best thing to do is cook up some long grain rice, let it cool, mix it in with some canned cat food such as friskies bits (any flavor kitty will eat. They won’t eat all the flavors). This usually sticks with them. They usually clear up from the runs, and often put back some weight over time. It’s something you’ll have to do until kitty is looking healthier, and you aren’t having to watch all the time.
Try a 1/2 cup of rice in the pot with 3/4 cup of water on low until the rice is done. About 20 minutes. Gotta watch it real close if cooking with gas. If it works for you as it has for us then you might want to make more each time you cook the rice up. Just depends. We are currently feeding three the rice mixture as they are all elderly, and have some digestion difficulties, runs, or some other disgusting malady, but we do love them so we do it.
When in was a kid I always had a cat. My mom didn’t hate cats, she just tolerated them. This one cat I loved became very ill with a cat cold, and we were too poor to take him to the vet, so my mom made him a bed in the bathroom (she never let him in the house) and made him chicken soup and he got well!