Can you help me with some problems I have?

When I was younger, I had a good life. I was honest, smart, trustworthy and grateful. Now I'm 13, and my life isn't going so well. My brother has a health issue (private) and I constantly argue with my mother. Me and my mom argue sooo much. I really can't take it any more. I've been a lot less honest and trustworthy. For an example, when she punishes me for cursing or something, I don't listen and I do it anyway. Then, I get in more trouble which makes me more angry which makes me curse. Then I get in MORE trouble for cursing. Also, my mom seems like she's always on my brothers side. She also is really strict on what I eat because sugar makes me hyper. But then I think "it's not fair! Why can't i be like everyone else and buy food I want to buy and other things." Also, she's constantly nagging me. All this is causing me to be grouchy and very moody and angry and untrustworthy and ungrateful and rude. I dont want to be this way but all of this is going to my head! What can I do?