We’ve had this issue recently with another member.. The problem with prescribing antibiotics to young kittens is that as well as kill the bad bacteria it also kills good bacteria in to gut making it harder for kittens stomach to get back to normal.. I’m assuming you’ve already wormed kitten.. If not this should be done to eliminate any parisite causing an issue..
Changing of food will almost always cause some stich upset.. You can use goats milk natural yogurt.. ( it has to be goats milk!) no cows milk product as this will cause an upset tummy.. Most cats are lactose intolerant so goats milk is the best to use..
This should help boost the good bacteria in the gut speeding up the healing process.. Also it’s high in L-lysine which really improves the over all health of kittens/cats..
Some people also suggest tinned pumpkin ( not pie filling) this helps with digestion too..
Finally eating a bland food ( boiled chicken/turkey) can sometimes settle a stomach.
Unfortunately these are the joys of reusing kittens 🙂