Welcome to YT and congratulations on your new puppy, Oliver
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I got my ZoE, who was a healthy size pup, at 6 weeks too...so very young for a yorkie puppy. Make sure you feed him frequent small meals to keep his blood sugar level. Our vet had us on a 4 hour feeding schedule for the first week. ZoE will be 15 weeks old on Thursday and is doing great.
Looking forward to seeing pics of Oliver.