7 month old pup losing weight

[dogcrazyforever]

Hello Everyone, I'm in need of some advice. My 7 month old AmStaff puppy had lost 4 pounds in two weeks but, other than that, he acts normal.
I took him to the vet and (even though he is on a regular worming schedule) had a fecal exam and full panal blood test done. Due to it's high occurance in my area, I assumed he had Valley Fever. However, all the blood work came back without any abnormalities and in the fecal, no eggs were found. My vet says he seems normal aside from being a bit skinny.
I'm at a loss now as I believe a dog his age should be GAINING weight instead of LOSING it.  But, he does act happy and energetic as he is ever is. (He's a couch potato until you take him for a walk, then he runs wild!)
Should I worry? Is there any supplements I can give him or something? Both his parents are NOT skinny dogs and normally he is built like a tank.
So what would you guys say?

[TINKSMOM]

Maybe its his diet. What are you feeding him? Quantity means nothing without quality. Maybe he needs more of "the good stuff" in his diet, less fillers, especially if he is an active dog. They can burn calories like crazy. You need to make sure he is being feed a good quality puppy food.