My Sophie had a lump like that. At 12 weeks old, the breeder told me it was definitely a hernia. When she last saw the vet (now age 6 months old), I asked about it. He checked and said he didn't feel anything and it must have been from the cord when she was born and went away. He told me that if she did have a hernia, they could easily fix during her spay surgery. He also said that as long as they don't seem to be in pain from it, you may opt to not have it fixed. I would have the vet look next time you're there.
