Why does my mom treat me like im such a horrible child?!!?

I honestly think im a good child. i stay out of drugs and drinking. im not a crazy girl. i stick to my morals. i have a full tuition scholarship for college. 4.0 student. im 18 almost 19 with a curfew of 10:30! im not allowed to go to clubs. im not allowed to hang out with guys. i cant talk on the phone after 10(even if im paying for it!) i have to ask for permission every where i go and sometimes she doesnt let me go! i have a part time job and i HAVE to give her 100 dollars out of every pay check! when i try talking to her and telling her that i need that money because i dont really earn much she gets REALLY angry with me and tells me that im so ungreatful and selfish and that i have no choice because she's my ride and that if i dont give her money she is not going to drive me to school or work. (i know im old and i should have a car, but my job doesnt pay me enough to afford a car) i have a stepdad who doesnt help me economically, my mom doest have a job so thats why i got my job to spend the money on MYSELF. but she just doesnt understand. i help her a whole lot around the house. i take care of her kids when she needs me to and i dont complaint. i just dont understand why she always fights with me, when i dont mean to pick a fight with her. i just wanna be young and go out and have fun, but its just impossible with her. she threatens me to kick me out of the house when i come home late (11:30 and 12:00 is late for her) and i have thought of moving out but i cant. not enough money, or anyone to move out with. i dont know what to do anymore. we just had a HUGE agrument over money. how she wants me to give her some when i only had 2 days of work for two weeks wich is nothing! :( i always try to be the best i can but im just so tired of everything! little things i do she makes it like a HUGE deal! sometimes i feel like doing whatever i want to do and not caring what she does or thinks but i do care. shes all i have. i dont know my dad. the rest of my family lives 2 hours away. im just so fed up with it all :( i dont know if im just overeacting but can anyone give me some advice?