Authority Trouble ???????????????

My mom is single and she is always riding me about being on the computer or something like that and she took away everything: my iphone, xbox, and complete social life. She wont let me go out with friends because of my grades. My grades have come up to passing and she still wont let me go out or have my stuff back. I thought that her having a boyfriend would cheer her up, but NO she cant be happy. She is always on me and im at the end of my pitiful rope and I dont know what to do. She wonders why I yell at her, well i wonder why she nags me all the time. i dont know what to do. My brother (19) is always on me too, him and my mom seem to team up and nag me the same. i dontknow what to do. my brother thinks im stupid i guess