HELP!! Kitten with diarrhea!?

So I have a kitten, and since yesterday afternoon he has just had diarrhea non stop. Im not sure how old he is since i found him but he has to be more than a month old now seeing as he eats, drinks and goes to the toilet by himself. He hasn't been acting weird, he is his normal self, he is eating fine and he is playfull. I have been feeding him croquettes for kittens and since yesterday afternoon he had no problems with them. I also gave him a bit of kittens milk today just to help his digestion. It cant be worms seeing as he doesnt have them in his poo. Does anyone have an idea of what it could be????