What Causes Blackheads Like Bumps On Chest And Back?

I am a 47 yr old female who recently started snorting crystal meth. A couple of times after using (a day later or so) I have noticed blackheads showing up on my chest and back. When I went to pop one of them, it got very painful, larger and would only secrete some liquid form. They were also raised. I have had blackheads in the past and these are not blackheads. I believe it is the meth coming out of my system. In the meantime (besides the obvious) what can I do. Will they just fade away or could it be some kind of skin cancer? Please advise.