What Causes A Hard Lump After Taking Vivitrol Injection?

Hi, I had an injection of Vivitrol in my backside one month ago (my 4th treatment), and unfortunately a few days after the injection a hard lump appeared that was very sensitive the first two weeks. This was the first time I ever had this side effect. My doctor who did the injection said it should go away on its own over the course of a few weeks, possibly a few months. He suggested doing warm compresses and hot baths to speed it up, but nothing seems to work. I m starting to worry that it will never go away. Is there anything that I can do? - Sincerely, Bummed Out.