When Tango was a young puppy, I was feeding her about 3 to 4 cups daily (depending on her activity level) at around 14 weeks. I can't remember what I fed when she was younger than that but probably around a cup and a half to 2 cups as she wasn't as active before she hit 14 weeks. Always three times daily too when she was young. She wasn't on a great food, as that was before I had internet and knew anything about food (she was eating Nutro Natural choice - not awful, but not wonderful). Either way though, even with a premium kibble, she probably would've been eating close to the same amount. Seeing as Tango isn't a large breed like a Golden (she's 35lbs full grown) and she required that much, I'd imagine that your pup would probably need the same amount or a bit more than Tango got as a pup. I'd definitely say you're under feeding her, but don't worry, I'm sure you'll have her at a healthy weight soon! Puppies need a lot of food. They eat considerably more than adults. As an adult, Tango now only eats 2-2.5 cups a day; big difference from when she was a pup.
The foods mentioned above by showpug are all excellent, and you should have great success with any of them. Most can't be found in chain pet stores usually. I know PetCo sells Natural Balance, but I don't think Petsmart sells any sort of premium brands. The others can always be found in smaller, privately owned stores.