Hello and welcome to the forum. No need to apologise for talking poo
it's a common theme! Lots of changes happen to a puppy so quickly in the first few months of their life. A change of food directly from one onto another has obviously not worked for him. You have done all the right things, talked to the vet, onto chicken and rice and back to the beginning with his food. If he is drinking plenty and staying hydrated I wouldn't panic too much. Cooked sweet potato is soothing on the gut, just microwave it until cooked and scoop out the soft inside and add a bit to his dinner. Pumpkin also works and you can buy it ready pureed in tins. Another thing as a standby is plain frozen white fish,, just the cheap basic one from the supermarket. I poach it in a fair bit of water and give them the water as well, it makes sure they are getting enough fluids. Things at the rear end will probably be 'loose' for another day or two yet. There are no hard and fast rules. Keep us posted and try not to worry too much, easier said than done, I know.