Re: Do I have a runt?
At 15 months, Savannah was eating more than the bag recommendations, too. I assume partly because of her activity level. Her kibble was mixed with wet dog food and, like MilesMom, we supplemented with people food - peanut butter, chicken, turkey, veggies, fruit, etc.
If you supplement with people food, I suggest you read a bit about what others have found regarding allergies. By varying the diet, if you do have an allergy problem, you will have to track food fairly quickly and carefully to find the source.
There is a recipe for satin balls on the forum that folks have used to increase weight. It seems to me there are a few other recipes that could also help. Redbirddog's liver treats come to mind. Use the search function. You should find some good ideas.