My puppy threw up un chewed food! Help!?

My little puppy is 3 1/2 months old. She was doing fine. I had just taken her outside for a walk and came back inside to feed her, then she went upstairs, and threw up. It was kinda gooshy, but the food was un chewed. she is a shih tzu and i only feed her about a hand ful and she didnt even eat all of it. Please Help