What should I do about a knot in the back of my dogs neck?

[Hershey1931]

My dog  has a knot about the size of half a tennis ball on the back of her neck. This has just apeared over night. We gave our female pit bull a shot about a week and a half ago and this is the first sign of trouble. The thing that worries me is that it's in the same spot where we gave her the shot. The shot contained : canine distemper,adenovirus type 2 parainfluenza - parvovirus  vaccine. It says live virus as well. If anyone has any advice please let me know asap. I did call the vet but they just said that the shot should have had side effects  a lot sooner and to bring her in. Money is the issue  right now or she would have went. I am beyond worried about my sweet little girl. She is an inside dog but does get to go outside. We live around plenty of woods and have lots of bugs that could potentially  cause staph infections . Please help us out with some words of wisdom!