Why does my mom treat me like this ?

Okay , so I'm a 13 year old girl & I have 2 other siblings : Both brothers , one who's 12 , and the other is 15. I swear my mom treats them better. So like we each have to take turns washing the dishes each week , so like my brothers do a horrible job at it and like hardly wash them when its there turn. so like the sink fills with dirty plates , but my mom just decides to wash it for them ! but when it's my turn , if she sees ANY dishes in the sink at all , then no matter what i'm doing , she yell at me to come downstairs and wash the plates ! Or like this one time for my older brother birthday , she gave him 200 dollars , but when all I wanted to do was buy my own digital camera , she had a huge problem with it saying that I was wasting my money. My brother was the one who used $50 out of the $200 to buy these stupid headphones! oh but of course , she didn't have a problem with it. Or like , she and my dad always complain and say I don't help out around the house. I do ! I do laundry every week & dry everyone's clothes when they just leave it in there like lazy bums. And I vacuum the house & sweep the kitchen. I do all this while my 2 ses of brothers just sit down , eat all day , and play xbox 360. And I get the best grades in our house. For the past year , I've had a 4.0 both semesters, And I graduated middle school with various rewards , and all i got in return for all that was my mom & dad saying good job and giving me a hug ? WTF ? if it were my brothers , we would have had a freakeen party or something ! She constantly bitcches at me and says things like your gonna make a horrible wife , you cant clean , cook , or do anything right ! Like omg , I try. And when I do something good , she never notices. Like during middle school , she never came to a single basketball game of mine for the school , but during my brothers bball season @ middle school , she came to all of his. Or like I'd been literally begging my mom to give me money so I can go watch a movie with my friends , and then she was all like see all you do is bother me and ask me for money , but when i ask you to do something you never do it ! But just a day after that , my little brother asked , and she was like ohh here you go & gave him a 20! I had to use my own money for the movie /: Or like I asked her for lunch money and she was like didnt i already give you some ?even though she hadnt , then she got all irritated. but then of course when my brother asked , she gave it to him with ease. Or sometimes she'll cook food for both of my brothers and not cook any for me and say that I have to cook my own dinner so I can learn how to cook my own food when i get older and have a family. If that's the case , then why the **** are my brothers not learning how to ? Like im not a bad kid. I never get in trouble at school , I have friends and people i talk to alot , and I behave in public when im with my parents , while my bafoons of siblings act like complete fools & emmbar themselves when we go out. sometimes I ask her things like why doesnt she make my bros do all the stuff she expects me to do and I tell her its not fair. and all she says is well lifes not fair , get used to it kiddo.Sometimes I wanna cry , but then I just suck it up and forget about it. I know my mom loves me , so her love for me isnt it the case. but she treats me unfairly. So I just want to know why my mom singles me out from my brothers?