Every now and then you have an injection that gives you more pain and it may last for days. Doesn't mean its necessarily infected. If it seems to improve from day to day it's probably going to get better. Keep icing it to relieve swelling.
FWIW, I had an infection in my left quad a few years ago. It was not red, and I did not have a fever. I did have cellulitis and severe edema in that leg though. I nursed it for 2 weeks before going in. It was not getting better obviously.