I have a 6 month old boxer, very thin? Help!?

If you can see his spine and his ribs and your vet says that she looks great, then I think you should take her to a different vet and get a second opinion. It wouldn't hurt to get another vets opinion on your Boxers weight! Eating, seeing bones and not gaining weight means there is something wrong and you need to find out what it is. Maybe a second vet can find something that the first vet could not! I feed two of my dogs, Zoe and Gizmo Innova Wet Food because they both have Liver Disease and the vet says that they cannot have any kind of Dry Food, due to it having too much protein in it for them. I feed my other dogs a combination of California Natural and Halo!