6 Week Old Kitten With Diarrhoea PLEASE HELP.?

So before i start yes i KNOW he is way to young to be away from mum but the previous owner refused to keep him and was mistreating him and his sister, i have taken both of them in and i am doing the best i can with them. they are both very energetic, lively and playful, using the litter box and have both been eating and sleeping fine until today the male of the two has got diarrhoea really bad and was eating this morning but at his last feed he did not eat anything and btw i have NOT given him cows milk at all, just water and KRM. He is still himself being playful and lovely. I have already made him an appointment at the vet for Monday morning but i was wondering if there was anything anyone could tell me to help him in the mean time, any help would be really appreciated. One last thing him and his sister were wormed for the first time yesterday, could this have anything to do with it? thanks in advance x