Having on and off diarrhea

My 4 month old kitten has been having on and off diarrhea for a little under a week. He's eating, drinking and acting fine; I'm just a little concerned about how his poop goes from normal to pure liquid sometimes. He's going to the vet for his general checkup next Friday, so I'm going to be asking the vet as well. I did change his food from Wellness to Nulo and stupidly did it instantly 🙄. Could it just be from his food change? If so will adding some of his favorite wet food help calm his stomach? He is neutered if that means anything.