lump on cats back?

Question
Maggie my cat is a 9 year old spayed female cat. She has never been sick before. Yesterday I noticed a lump on the middle of her back almost on her spine. This evening it seems like it maybe is larger than this morning. It is soft if you push on it to hard she will flinch. She doesn't seem her normal self. She is still eating and drinking normally. We thought maybe she may have fell and hit her back and it's swelling. I was going to wait a couple of days and see if it gets smaller then I was going to take her in. Do you have any idea what it might be? Especially to show up virtually overnight.

Answer
Debbie, I would have a Veterinarian aspirate the lump to see if it is only a seroma or lipoma, or something to be concerned about.  When were her last vaccinations, and where on her body was she specifically vaccinated?  It is probably nothing to worry about, but is worth checking out.