My 3 month old puppy has a bump.

Question
My 3 month old puppy has a soft, moveable, bump that is usually on the right side of her neck or the middle close to the spine. I love her so much so I freaked out when I felt it. I googled as many topics I could and came to the conclusion that it is probably a Lipoma. It is about the size of a peanut from a jar (not the shelled ones). Tomorrow or monday I am taking her to the vet. I also read that it is common in weiner dogs which she is mixed with. The only weird thing is that every single thing I googled except 1, said that it is rare in puppies and occurs mostly in older dogs. Is it always a fact that they get bigger? Could it go away with a different diet? I just want to make sure that everything will be okay :(

Answer
It would be very unlikely for your 3 month old puppy to have a lipoma. Most likely what you are feeling is a vaccine reaction. This is a typical location for vaccines to be administered and it is not uncommon for puppies to develop a sterile seroma(fluid pocket) at the site of the vaccine. Was your pup vaccinated in the last 3-4 weeks? If it is not from a vaccine, it could be the site of microchip implantation. Did your puppy receive a microchip implant from the breeder or at the pet store? This is another common cause of seroma or granuloma formation. It is certainly best to have it checked by a vet but I would not be overly concerned at this point.
Dr. G.