Your mother is being cruel and seems to be deliberately undermining your self-worth. Has she always acted in this nasty way or is this behavior new? If she’s been this way throughout your life, then it’s time to get away from her until she seeks professional help. She either needs to attend therapy sessions or take parenting classes. Until she gets the help that she needs, go live with your dad, your grandparents, an aunt, an uncle, or a friend’s family.
If this is new behavior, have a heart-to-heart with your mom and ask her why she’s calling you names and acting so mean. Explain to her how hurtful it is and how it’s destroying the relationship and wreaking havoc on your self-esteem. Hopefully, she’ll open up and explain why she’s being this way. Perhaps, she had a weight issue when she was a teen and that’s why she’s hyper-focused on your body now. Perhaps, she became sexually active at a young age and is wanting you to avoid that same fate. Whatever the reason, her actions are misguided and she needs to change the way that she’s parenting.
Please talk to a trusted adult about what’s happening in your home. It’s not right, and you shouldn’t be navigating this on your own. Your mom has problems that she needs to deal with and another adult can make sure she does so.