bite golf

My 6 months. burrow years has a bump on the opposite side of his leg. Does the size of a flattened golf ball.
I just took him to the vet about 4 days after vaccination. The package was presented yesterday. He acts normal and does not scratch. felt hot to the touch. What could be? A possible reaction injections or an insect bite? If yes, how an insect bite swell so big? It does not react if I touch and movement of land. All First, he noticed three days after vaccination. Is firm, not soft. Thank you all for your responses.
Call the vet and say respect. Nobody would be able to help here. It seems very serious. But do not take chances. Call the vet. It could be that you hold the shot. My Chihuahua is a small bump that is slaughtered.
Callaway HX Bite (Dozen) Golf Balls