Hi there, New to all of this

Dont read ahead if your having food or have a dickie tummy!

Bascially my 13 weeks old Cocker has been suffering with diarrhoea for the past 3 days, his stools have always been abit on and off- he was on James well beloved, but his trumps were violent and his stools were very soft.
I then put him onto Ian WainWrights (i feel a bit conned here, its an expensive food- next to James well beloved in pets at home, well away from the cheaper brands, but unfortunately is a very cheaply made food

which i have since discovered, this food gave him very bad diarrhoea, like water almost. I starved him for 12 hours, his stool returned firm, fed him again, rest of the day water. Once again, and the same happened, i have done some research on food and i have now got him on Collards salmon and potato. (Luckily pets at home refunded the £40.00 i paid for the Ian WainWrights food without question or receipt)
Hes very well in himself, he hasn't changed any behaviours - energy.
Due to diarrhoea i have been giving him plenty of water- occasionally with 2 spoonfuls of sugar and a pinch of salt dissolved in, just to keep him hydrated.
Does anybody have any suggestions to help him get through this? If he hasn't cleared up by friday i will be taking him too the vets, iv stopped taking him for walks until its sorted, because when he poo's i can't pick it up its that runny and i feel awful if someone was to stand in it!!
Very frustrating, especially because he seems so well in all other ways.

Thanks
xx