I went through a similar thing when I was a child, except my mother also used to scratch so hard she'd draw blood, and spit in my face and scream so loudly directly into my ear that I now have permanent hearing problems in one ear. It started out the way you're describing it though :( I felt like you but didn't get the help I needed, and ended up attempting suicide when I was 17. She still uses the suicide attempt against me ten years later and jokes about how I'm such a screw up that I even failed at killing myself. PLEASE do not let things get to that point - I don't want you to end up like me!
Please document your marks and bruises by taking pictures of them on a camera or your phone (if you have one) or asking a trusted friend to take the pictures and email them to you. If you are still in school, your school counselor or pretty much any teacher is obligated to take action if there's any suspicion of child/adolescent abuse. Show the actual bruises if you still have them, and the photos you have. Tell them what you are going through, and that you tried to reason with your mother and avoided doing anything that might trigger her, but nothing helps. If you are worried that your mother will retaliate against you for reporting her, tell the teacher/counselor about your concerns about your safety. Ask them if they are going to write up a report, and if you should get a copy to show to the police because you're scared about your safety. They will take you all the more seriously if you make it clear that you expect them to do something to help you.
My suggestion is to go somewhere quiet and think about what you are going to say before you talk to the teacher or counselor, maybe write it down as a statement. You need to make sure that you communicate carefully, because often times young people are accused of being hormonal/emotional and blowing things out of proportion. It's up to you, but I would focus on the following things: public shaming and bullying regarding your weight and acne, her inability to manage her anger/uncontrolled outbursts of rage, and physical abuse... but leave out how she nitpicks the way you do laundry or whatever (because ALL parents nag about that stuff and that's not abuse!) You need to emphasize that she does NOT use her words and physical contact in the context of discipling or advising you, she does it to make you feel small and intimidate you. Some authority figures unfortunately believe that a little bit of physical punishment is a legit form of parental discipline and might not take you seriously if you just say "mom says mean things and hits me sometimes." However, if you emphasize that her actions and behavior are well beyond the realm of any well-meaning parenting style, you will get better results.
I'm not trying to scare you, I'm just trying to tell you all the things I wish an adult had told me back when I was growing up. I have three final pieces of advice for you: 1. Specifically tell an adult at your school that you are feeling suicidal because of your home environment, and ask if there's any way to get psychiatric help/counseling (trust me, it's really helpful.) 2. Pack a small bag/backpack with one change of clothing, clean underwear, toothbrush/toiletries, and any other necessities that you might need for an overnight stay somewhere and keep it somewhere that's easy for you to access in an emergency, and 3. If the school was unable to help you or things escalate to the point that you're in serious danger, grab the bag and get yourself to the nearest police station for help.
I'm praying for you, and hope that you get the help that you need.
Don't talk back, that's all you have to do. And yeah you're mom is being a b****, I've went through the same thing w my father. Criticized me on everything, but don't take it to heart. They are unhappy with themselves. If she's hurting you like my father did to me, than leave. Call the police and leave. We can't help you. At all. Take that sh** in your own matters Bc we can't do anything about it. How about you actually stand up for your self and leave? Idk what else to say to this but you'll get through it. I hope everything goes well (:
She's unhappy with herself and is taking it out on you. A lot of parents try to live vicariously through their children, but if they don't see their children in a positive light, then it messes up their "living vicariously" thing. You're being abused and should probably find a way out. Don't try to be perfect, don't let her ideas control you.