I wasn't sure if I snagged some ugly scar tissue after an inject but it turned out to be a small infection. Injected in my glute and it got a bit sore too (not as sore as my quad).
If the inflammation had kept up I would have went to the doctor to get it checked out. If it's getting inflamed and isn't showing signs of slowing down, just head to the doctor. Don't order antibiotics. If you have them on hand, take them. I had them but don't want to abuse them (ironic statement, eh?). Definitely not something that you want to be liberal about.