My mom says particularly negative things at every turn, sometimes in a sour way that makes people uncomfortable. She also always picks on people as if it makes her happy.
She wasn't like this when I was a kid, but since I started middle school, she's gotten worse. She kept saying that I was "fat", "nothing like me", "ugly", and even "you'll be picking up garbage". I even said, "You can only pick up garbage from now on. When she saw some shabby pedestrians on the side of the road, she secretly laughed at them and then turned to me and said that I would be like that in the future. Then she said that I would be like that in the future, and then she would criticize me and tell me that I would not be successful in the future. She even used my privacy as a joke and told people about it. But every time I refuted, she just ignored me and kept talking.
I especially don't agree with her doing that, so we fight a lot. I'm not even as bad as she says I am, and other people's plight shouldn't be a laughing stock. But she never listens to me and always thinks she's always right. I really don't know what to do with her anymore.
Sending you a hug first. It's really hard to stay in an environment that is bursting with negative energy every day. Especially when that negativity comes from one's closest mom, the pain is doubled.
Why does your mom keep putting you down with negative words? I think there could be two reasons.

First, your mom may have a particularly low self-esteem inside. She finds balance and fulfillment by ridiculing and belittling others. You are her daughter, so naturally you bear the brunt of this. As you slowly grew up and had your own ideas, she was afraid that you would look down on her and not listen to her, so she had to suppress you even more to retain her parental authority. That's why "she's been getting more and more overbearing since she started middle school".
If that's true, then your mom is actually kind of sick, as in sick. You have to be sympathetic to her pain, in addition to studying hard, watching your figure, and helping with the housework. Just ignore what she says and don't take it personally. I know it's especially hard, but when mom is sick, we can't compete with the sick, right?
Secondly, your mom may not be happy with you and is trying to use agitation to force you to become what she ideally wants you to be.
If this is the case, I suggest you have a good talk with your mom. Tell her that you understand her good intentions and will try to get better. But what you need is encouragement and support, not cold words to demoralize you. You could even say that she brought you up herself and that by demeaning you she is actually demeaning herself. This kind of aggravation doesn't do anyone any good, you can try something else.
I hope the above two points help you.
May you be treated gently by your mom.
I'm Aunt Jane. The world and I love you.