Who does the food shopping in your house?

..I'm 16 and my mum expects me to do it and not just talking about a loaf of bread i mean the whole lot..all the frozen food everything drinks milk etc. Im just really angry. all she does is complain blah blah blah and expect there to be change from �20 for about 2 weeks worth and half the stuff i dont eat. I have 2 two brothers just now she told me to go and buy rice.. not a small packed but like a huge bag.. its embarrassing and its not like she doesn't have a car. I want to leave.