Have A Lump In The Arm. Have Been Using Drug Very Excessively. What Can This Be?

I am an IV drug user and am having issues in my left arm since a dose last week. There is a rock hard lump in my left arm. I wasn't worried too much because I'd read it could just be a blood clot. But the past two days my left bicep above the injection point has developed a quarter red spot that has now turned into a fully inflamed/red bicep from the quarter sized. I also feel two more late hard lumps above the injection site. I need an idea what this could be and what kind of medical attention I need. Thank you