Sore Injection Spot

here’s the deal. i pinned left glute right glute left glute, alternating everytime. the second time coming to the left side it was still sore i had thought nothing of it but maybe a bad injection, so i just went back more and injected. few days later the first injection spot started getting red and hard and about a week later i finally got into the hospital to find out i had a infection and abscess. i got it drained, took antibiotics. this was 3 weeks ago i got it drained. now that spot does not hurt at all. it’s behind it where i pinned the second time that is sore as hell. it is not red there is no lump i have no fever. i’m wondering why it’s so sore? i have not pinned since that shot