I'm 20 Years Old and my Mother Treats me Like a Child

this is somewhat of a rant but somewhat of me asking for advice. this is not me being an ungrateful millennial, but me being a frustrated adult who isn't being treated with the proper respect that I really feel I deserve. I go to college 5 days a week, and I pay for all my classes and books and gas for my car. I bought myself a new phone with my own money, and my mom told me I could keep my phone on her account, which I am grateful for. My mom needed help with a few bills, so I helped after being promised I'd get the money back. I spent a few hundred dollars on books for my 18 year old sister because she couldn't afford them and my mom again could not afford them but promised to pay me back. I had to schedule my classes around my sister's classes because she refuses to drive, so I have to drive her to school. I have to pick up my 13 year old brother twice a week from his school (my mom only picks him up once) and he tries to distract me on purpose when I am driving. I ask him to stop, but he does not stop kicking my seat or screaming in my ears or calling me a "fat piece of sh*t" so today I told my mom that I can't do it anymore. I told her she can ask the lady that drives him home the other two days to drive him home on my days too. and she told me that "this was all part of the deal and that if I don't drive him then I don't get my car. a deal that I never agreed to, and a car that I completely pay for. picking him up from school takes an hour and a half out of my day. an hour and a half that I could be using to work a real job, or do homework or study or something productive other than sitting in my car wasting gas only to get abused by a 13 year old boy. I feel like I'm being held back and I have no way to break free and get the respect I feel I deserve.