What Breed Is My Dog?

We bought this little guy about 7 months ago. The lady said he was a Chihuahua and Pomeranian mix and would not exceed 8lb when fully grown. He was tiny when we got him, about albs. Well he is now about 8-9 months and weighs about 15lbs! Maybe he is just fat but.. His ears are floppy and have never popped to become pointy like normal Poms and Chis.

I think the lady lied to us, but we love him now and never regret buying him. We believe he will probably grow towards a medium sized dog, but that he has to be mixed with a larger breed somewhere. Please help. He grew up to look nothing like a Chihuahua or Pom! People look at him and ask if he's a baby Retriever or Labrador. We tell them he's about 9 months now and we don't know what he is!