I had an infection in my shoulder and upper-arm that looked like green, black and yellow ink under my skin. The site was rock hard, and I got the worst case of strep throat I have ever had. I used some Cephalexin from an aquarium supply to suck the puss out.
Even though I didn't do anything wrong during injection, sometimes stuff just happen, I guess I was unlucky. The dumbest thing I did was not going to a doctor. Although everything turned out all right, I could have lost my arm or worse, died simply because I was too paranoid to ask for help.