Sounds like infection or parasites to me so definitely a vet trip. Stool sample would be the only way of determining the exact cause.

Any update, where are you located, there is bound to be some provision of out of hours vet care if not with the one you have been using, with another, is a little difficult to believe somehow, am being completely honest with you.

You have expressed your concern for the kitten however we have advised the kitten needs to be seen by a vet so to determine the cause of his condition and for him to be treated properly. If he is poorly with an infection and or whatever the cause, understandably his stools are going to smell!!! YOU NEED TO SEEK VETERINARY ADVISE and the longer you leave it, could result in serious implications for your kitten. You seem reluctant to listen to what has been suggested to you and continue to DIY, after five days it's not working, perhaps you need to seek another approach for sake of kitten, that is to get help from a VET who can tell you what is the cause if this is I quote 'I just wish i knew wots causing it' and this is your genuine concern. You seem to be quite casual about it all

If your regular vets aren't answering, then you need to find another one. 5 months isn't tiny, but still young enough to not let things drag on too long. Kittens can go downhill very quickly from diarrhea. The fact that this problem has gone on this long is worrying in that your kitten can only be getting weaker. Please, please, find a vet!

__________________
My babies
Aber, Ragnar, Kelso (the corgi trio), Daisy (our rescue mystery-mix puppy), Ellie, Henry, Gwennie, Jezebel (the kitty quartet), Blake, Chaucer, Molly and Milton (the kittens), and Bingo the African Grey parrot

Over the Bridge:
Pippin: 1/6/08-17/5/11
Freja: 11/8/10-30/10/10
Kirby: 11/8/10-1/11/10

"Praise liberty/The freedom to obey/It's a song that strangles me/Well, don't cross the line" Billie Joe Armstrong