A new puppy should be seen by a vet regardless, but especially when things don't seem right. A puppy that young go downhill VERY fast.
Also, that is very young. In most states in the US, it is illegal to sell or give away a puppy that young. I understand you're not in the US, but it's still a really bad idea.
Also, that is very young. In most states in the US, it is illegal to sell or give away a puppy that young. I understand you're not in the US, but it's still a really bad idea.