Sorry to hear poor Dodger is still poorly Kat. It may be an idea to take in a urine sample as well as a stool sample. Evie was very poorly as a puppy and although Dodgers condition is probably totally unrelated to Evies my experience has shown me not just to look at the obvious i.e his upset stomach. You mentioned he has started to wee in his crate - it may be worth checking he hasn't got a urine infection.
Our Flat Coat Murphy had very bad gastroenteritis when he was 3 months old and we nearly lost him. For a long time after that it took me quite a while to find a food that suited him. Duck is quite a rich source of protein so maybe something lighter like chicken or fish and rice based foods may suit him better. The food that has worked wonders for Murphy is Burns Pork and Potato for sensitive stomachs but other brands do foods for sensitive stomachs or dogs with dietary intolerances. Our friends pointer always had digestive problems and they finally got him settled on cheap and cheerful gusto for working dogs so I guess it is just finding something that suits your dog.
I do hope you get him settled soon as I know how worrying it is when you can't seem to find an answer and you have a poorly pup. Atleast he is a good weight so keep positive and you will get him sorted.
Lovely pictures from everyone. Wish the time was right for us Ali as I would love to have baby ziggy - they all look lovely!