I am sorry Louis has an upset tum.
The important thing is that he is alert, bright, happy, keen to eat and not vomiting. If he is unwell, vomiting or dull then you should pop along to your vets for a check up of him. Otherwise, it may be a simple upset from something he has eaten, or possibly a tummy bug. I would make sure he is upto date with worming as these can cause upset tums. Then I would starve him fro 24 hrs, providing free access to water. Then introduce a bland diet that has a protein source and a carbohydrate source in ti, try to feed something he has never had before. So, low fat cottage cheese, scrambled eggs, turkey or white fish along side something like mashed potatoe, sweet potatoe or pasta. Hopefully things will slowly improve. You could also add a small amount of live yoghurt to his food, maybe a couple of teaspoons to help his digestive bacteria.
I forgot to mention with regards ***** ***** I would use Panacur (fenbendazole) once a day for 5 days, this will treat worms and also protozoal parasites which can cause diarrhoea.