Small lump on cats back

So Callie who is actually my sisters cat is now living with me because my sister is going to move in here in a few weeks after my current roommate moves out. But she took her to the vet at the end of last week for a sore that had appeared on her neck and to get her shots and I wanted her FIV/FeLV tested before she was allowed around my cats so she had that done as well. Callie was negative and the sore on her neck the vet said was an allergic reaction to something so they gave her a shot of antibiotics. It is clearing up nicely. But now I have noticed a small lump under her skin between her shoulder blades that was not there when she went to the vet. What I am wondering is if it could be from any of the injections that she got, I don't know where they gave them too her at because they did them in the back when the went to do bloodwork and shave the spot that had the sore. I don't know if I should worry about this or if it is from the shot and it will clear up on it's own.

It could be from the injections......I usually notice this on my pugs when they get their annual vaccines. It usually starts to get smaller and then disappears in about a week. Keep an eye on it - obviously if it starts to get bigger or looks worse I would have it checked out.

yeah its a little smaller than a marble, the main reason I just don't know is all of my cats have had vaccines in their back leg and I have never seem a lump appear afterwards. If she got it in her back it will be a new one to me, but it is not getting bigger so hopefully it will disappear soon.