Oh and I am feeding him Purina One Large Puppy.
That might be the problem. It has a lot of fillers, that's why you have to feed him so much. Check out the info on this forum on good brands to feed and to look for ingredients to avoid.
You will pay more for each bag but also feed less and scoop less waste.
Deja, GSD, sable WL, female, born 11 / 2013
Cam, Rough Collie, sable, male, born 8/2015