Need help, mother abusive? Don't know what to do

I should start by saying that a year ago my mother found out that my father (technically my step father, though he's practically the only father I've ever known) was cheating on her with a 26-yr old known prostitute. They actually had/have a relationship, it wasn't just a one time thing for him. This happened before my 16th birthday. My father was a doctor and my mother a nurse. I have a little brother who is currently 3. My father's girlfriend for some reason found it hilarious to send us threats and tease us and make our lives Hell. My mom wanted answers from my father, like why he did it. He wouldn't tell her and for some reason she started digging around for background information on him. She found a bunch of illegal things he'd been doing and since then she's gone a little..crazy. I think. She claims we're being poisoned, that someone is going to kill us, that our lights in the house moved into contain cameras, that there's a gas leak, etc. I believed her for a while..but for the past few months if I disagree with her, she gets really mad. Mad enough that she'll hit me. There hasn't been a lot of incidents where she actually physically harms me (kicked me once, while I was hiding from her on the floor under a chair, slapped me because I was crying, hit me with a metal-flexible lighter across my arms and chest, pushed me multiple times, and hit me a few times..all of these were on different occasions) but on a daily basis she calls me ugly, a *****, a ****, tells me I'm retarded because I don't believe her, says she hopes I die and that she hates me, that she's disappointed in me, that it's my fault my father cheated on her, that I'm crazy, and once she said I shouldn't have been born. I should mention that up until the divorce my mom and I were very close. Almost like best friends. The situation with my little brother isnt much better.. She hardly watches my brother.. I assume she does when I'm at school, though often my grandparents have him. As soon as I get home, he's my responsibilty. He sleeps with me every night and my friends have commented (the ones that know partially what happens when I'm at home) that I'm more like his mom than she. My only escape is school and even them i'm not truly "free". For the past week she wouldnt even let me go to school. I finally went against her wishes because im taking college level classes such as Precalculus and an AP US History class combined with an Honors English one, both of which are rather challenging and when i miss them, it messes with my grades. My father isn't involved with us, at all. He is virtually unreachable. My biological father is the same. My grandparents dont know about what my mom does and says to me. I feel that it isnt right..am I being abused? I don't want to tell anyone or call CSD.. she's my only parent now. I don't know what to do.. i can't become emancipated because I have no way to finacially support myself. I can't drive because my mom won't take me to get my permit (she says my bith certificate was stolen). I should also say that sometimes I say things I shouldn't and that I sometimes forget to vacuum and unload the dishwasher.. she tells me I'm the worst daughter ever..am I? I appreciate any help.. I often wish I had a way out.

Please tell your grandparents what is going on, and please let your guidance counselor or a favorite teacher know, too. Your mother's behavior isn't because you forget sometimes to unload the dishwasher. She needs to see a qualified doctor as soon as possible. I'm sorry this is happening, but it isn't your fault and you and your brother deserve help from caring adults. Please seek out that help.

I agree with IceCreamKid -- there is something seriously wrong with your Mom. I don't know if she's mentally sick, or if she's on drugs, or what. But you and your brother need help! You ARE being abused, and you need to tell your grandparents AND the school counselor! You need to live with your grandparents or something, but NOT with your mother! At least not until she gets some help!

I wish you the very best. Tell someone as soon as possible. God bless and take care. Hugs, Lee