I have so many different things swirling around in my head that I don't know where to start. I feel like my heart is just going to stop any minute.

I am seventeen years old. My mother is angry all the time. All the time. I was raised by my grandmother, and I never saw my mother or my father very much until I was at least ten years old. And I really, really wish it had stayed that way. I am miserable every day. She is always angry, nervous, yelling, screaming. It never ends. Ever. I know I'm not being a selfish bratty child, because she is just as abusive to my grandmother as she is to me. I have battled anxiety my whole life. My depression started when I was 13, and has gotten steadily worse. My mother thinks I'm stupid or something.

I have been in a very similar situation, your mother must have a chemical imbalance and this is NOT your fault. Try to ignore it like I did and go on with your life .Try to keep yourself busy with things you like to do, it would be great if your mother seeks the help of a professional .If this doesn't happen like it did in my family , you will have to make your own life outside your parent house, meantime work toward what you want and what makes you happy.and whatever your mother tells you say OK even if it is not true, By answering her you make things worse keep yourself calm and follow your aim.
Hope this help