What Causes A Lump After Getting A Vivitrol Shot?

Hello. I got a Vivitrol shot on June 9th (so now its a month and a week) and somewhere around July1st I got a half-tennis ball size lump at the injection site. It is mildly painful, but it has seemed to get harder and doesn t seem to be healing. (I really love Vivitrol, because I ve been enjoying my first month of no hangovers after forty-five years of four hangovers a week!). My beloved Doctor didn t want to give me another shot until this was sleuthed-out. I am waiting to get a cat scan appointment. What I want to know is: What is the lump made of? Is it at all dangerous? How long will it last? Thanks for your help Suzy Williams YYYY@YYYY ,