My puppy wont eat! Help?

He's young, anywhere between 4-6 weeks. He's a Peekapoo puppy. My mother and I bought him from a flea market, and he was healthy, that's why we bought him. (he had paperwork to prove he was healthy.) It's now 1:06PM, and he hasn't eaten since a little after 7AM. Don't know what to do, please help.