How do i get my mom to stop doing drugs?

Okay so my mom has been acting strange. She always used to make me pee in a cup for her before she went to work, she used to go out a little and now its turning into every night. She makes me watch my younger brothers while she goes outs and parties. I know she is buying drugs. I'm positive shes on Oxycontin. I think shes on cocaine too, and prolly other stuff. One day she got off the phone with someone and asked me for 40 dollars and said she needed it right now. Another time me and my brothers were playing scrabble she went upstairs and came down her voice was different and she was hallucinating. I told her to go upstairs or i was gunna call 911 but she wouldnt. My little brother went and got the phone and called. As soon as he said "my mom" she took the phone and was completely normal her voice went back and everything. To this day i still have NO idea how she did that. Everytime i try to talk to her she denies doing anything. Today i watched her hand some girl money and take and envelope from here. I am constantly finding empty pill bottles with no paper on the sides in her room. I also find little empty baggies some white substances at the bottom. She always bringing guys home and having . She even did it with my 6 year old brother in the bed asleep. She just seems like she doesnt care anymore about anyone but herself. Everything is wearing me down. I cut myself almost every week. Im tired all the time. All i wanna do is sleep because im always happy in my dreams. I want to tell her i cut myself but i dont know how to do it. I told my dad about her behaviors and he says he cant do anything. He only has a ONE room apartment. I dont wanna go into a foster home. Im only 13 and i have two other younger brothers. I dont know what to do. Please help.