This is one of the reasons I never inject any gear brewed by someone else without first letting it cook for 30 minutes at 200 F to make sure there was nothing viable if there was any bacteria. I don't give a shit if it effects the quality of the compound, abscesses are nothing to take a chance with.
If you suspect an abscess, it's warm to the touch, red. I wouldn't wait for our advice I'd go see a doctor that can check it out and get you on antibiotics. I've seen some gnarly abscesses from IV drug users that had a lot of meat cut out of their arms.