Hi and welcome to YT

- really glad you found us

! I feel bad for you, bc you do have a really young one here, and that puts you in a tough position bc they're just so vulnerable at this age. Just keep doing what you're doing in terms of being vigilant about eating and drinking, keeping a close eye on things, and taking him to the vet if anything goes downhill.
For food, I'd discontinue the milk as cow's milk isn't really great for puppies (as you've seen), and I'd instead try sprinkling some Parmesan cheese (the powdered kind) on his dry or wet food to entice him to eat...Parm is nice and pungent to dogs.
I hope your little one continues to do great!