Kitten with diarrhea

One of our kittens(5mo) been having diarrhea for almost a week (ever since we picked him up from our friend that was cat sitting for us), they said he was doing fine the entire time.

We brought him to the vet, but they didn’t find anything wrong with him, he is still eating and drinking fine, just all diarrhea and no solid poop, he also started to diarrhea on our bed…

Any advice would be much appreciated!