Lump on kittens back inbetween her shoulder blades 14 weeks old ?

hi i have a 14 week old kitten she had her 2nd jab on friday the 20th may , she has a lump inbetween her shoulder blades about the size of half a ping pong ball noticed it about 5 days ago, it doesnt cause her any pain and it doesnt seem to be attached to anything when i feel around it . any ideas would be great ive got a vet appointment on thursday this week but any thought would be great ..