my clothes don't fit

I am a size 4 of jeans. I like high waisted pants because they cover my stomach fat. This probably sounds like I'm being dumb and want attention but I really don't know what to do. The majority of my clothing is hand-me-downs or free t shirts that you get at events. I have like 4 pairs of size one jeans but they are all too small and I have to wear my brothers sweatshirts(my mom bought them for him because they say our school name on them) because I only have youth large size shirts and they don't cover the top on my jeans. My mom just spent $350 on my brothers senior pictures and she told me that we can't afford to buy Christmas presents anymore, so I assume that she won't take me shopping to buy clothes. And even if we do go shopping, if I pick up a 4 in jeans and put them on the buggy, she will put them back and get a smaller size when I'm not looking. Then when I try them on, she gets mad at me and calls me fat and she makes me feel so bad about needing a size up that I'm afraid to try them on because I don't know what she'll say. I don't know what to do. I need a whole new wardrobe basically because I've had the same clothes since 6-7 grade(in in 10) but she we don't have money and she makes me feel too guilty to buy any clothes.