What Causes Red, Sore And Painful Spot At The Site Of Injection?

I got a shot of toradol and a shot of rocephin 3mnths ago, one in each arm. One of those injections has caused my arm to sometimes have a small red spot at the site of injection. It has also made my arm VERY sore, painful if touched or pressed on. Why and how long will it take this to go away?? I would think three months would have been plenty enough time to heal. Could there be something wrong?