My Boyfriend Shot Up Meth In His Forearm, (over A

My boyfriend shot up meth in his forearm, (over a week ago) and he has hard lump, that is red and he said it is warm to the touch. I keep telling him to go to the doctor, but refuses. He said the pain was initially so bad to even rub even a feather against, but the pain is decreasing finally. He said the lump is getting smaller, but harder. What could this be?