My mom is always so negative and upset?

I can't do this anymore. I am 17 years old and I have read a lot of books that have improved my mentality and have helped me deal with her and her attitude but I don't know if I can do this anymore. Let me give some background information. My mom is a very negative person. I have noticed this since I was a little girl but I didn't know any better. When she gets upset, she lets everyone know. She slams door, yells, talks under her breath. It's just annoying to know that every time I walk into my house, there's a 96% chance she has something to complain about. Today, I had softball practice and I got home a little late because my friends and I decided to hang out since I'm always working on the weekends. As soon as I get home, she yells at me because I didn't help her clean. 1. I have a younger brother (15) who doesn't do anything at all yet I'm still to blame. 2) I'm never home. It's not like I party or anything. I'm usually either working, volunteering, playing softball or at school. I use my Friday nights to hang out with the same person and I always keep my room clean since it's the only place I'm ever in. I just don't get why she's always so angry. I've tried to talk to her about it but it doesn't work. She's happy occasionally, but it ends rapidly. I just wish I came from a more family oriented home. I yearn for the feeling to be wanted by my family and go on trips and go out to eat together. I never want to be like my mother but I also don't want her to live such an unhappy life. Please tell me how I can help her and make her attitude change a bit.