I'm not sure about the infections but I do know that the baby should not be given puppy milk. Baby guinea pigs can eat solid food from the day they are born so just make sure he is eating pellets and veggies. As for the bleeding I would definately take him into a
cavy savy vet and get him looked at. This could be serious. If you think he's having problems eating the pellets you could make a pellet mash. Also, if he refuses to eat, you need to hand feed him critical care or a pellet mash. This link should help
http://www.guinealynx.info/handfeeding.html