Feeding an 11 Week Old Pit Bull Puppy?

My son got a 8 week old Pit Bull puppy. He was feeding her a cup of dry food in the morning and a cup at night. She would gobble her food in minutes. She is now 11 weeks old and does not seem nearly as interested in food. She went from 8 pounds to 14 pounds and seems healthy. She probably eats about a cup and a half a day now. Should we be concerned? She drinks lots of water, but seems not as active. She is up to date with her shots. Her next set is July 8th which will be her 3rd set of shots. Thank you!