How can I treat depression on my own without medicine or therapy (neither are av!

I'm a 17 year old girl and have been dealing with depression for months now. I know it's not just like a phase I'm going through. I've read about chronic depression and have all the symptoms. I really miss the way I used to feel. In late 2008 my family moved to Australia for my dad's work, and my life turned upside then. My mom and I were in a car accident, and at the hospital she found out she had brain cancer. She's fine now, but basically is addicted to the pain killers that she took when she hurt her back and totally unlike the way she used to be. She's not emotionally stable, and she makes us all miserable. She had my baby sister last year, and does absolutely nothing to take care of her. It puts a huge pressure on me. My dad asked me to start going to school online to take care of my younger siblings and things around the house, so I'm basically like a hermit now. He does pay me a nice amount now, but it doesn't make up for not having a life. In Chicago I was an all-star (competitive) cheerleader, did gymnastics, and was popular and had a 3.9 GPA. Now I have few friends because I can never go anywhere. I do still get exercise every day, but not nearly as much as I did when I was cheering and doing gymnastics. I eat really healthy, and I take a multivitamin. I don't know what else I can do to feel better. I just wake up every morning thinking about how much I hate my life.

I asked my mom about going to see my doctor to get antidepressants and she just mocked me. I asked about going to therapy and she said no and that it was selfish of me to ask. I talked to my dad but he's super stressed out with work and can't help me.

What can I do to feel better? I just make myself feel numb so I don't cry all day.