kitten with soft stools

Hello, I'm new here and I need advice for my kitten, Rocky.  He's about 8 months old, we rescued him from our local animal shelter.  When we first brought him home, we fed him Fancy Feast, and he seemed to be doing fine.  Since he was eating so much and the cans were so small, we switched him to Friskies.  He liked it, especially the ones with the gravy, however they did not agree with his stomach and he developed soft stools.  We had him tested for parasites and he tested negative.  Our vet recommended we try Forti Flora, which we did.  At the same time, I also did research and realized that Friskies may not be the best food for him, so we tried Wellness brand pouches with the Forti Flora, and everything was normal.  After about a week, however, he refused to eat the Wellness.  I have now tried Iams, Blue Buffalo, Natural Balance, Royal Canin, all of which he did not like.  He has been eating Weruva and enjoying it, but his stools are still soft.  I don't know if it's because we've been switching him so much, I just want him to be better.  If anyone can offer any advice, it is appreciated.  Thank You!

to TCS! That's a common problem with our fur babies, and there are quite a few threads about soft stools here that you could take a look at.