I can't control my anger.?

I have a really bad anger problem. The slightest thing can set me off, like when someone doesn't close the door or when someone isn't listening and I have to repeat myself. My younger sister is the worst for setting me off. For example, she needed help on something so I helped her but all she did was push me away, etc. This really annoyed me so I started arguing with her and eventually hit her. She, of course, hit me back so this just carried on. I can't stop myself and I can't walk away because I can't deal with the feeling that shes had the last word so I carry on until I 'win'. Its got to the point where suppressing/ trying to suppress my anger causes my head to ache and I feel like I'm burning inside. I don't know what to do. Any ideas? (By the way, my sister is 5 years younger than me) Thanks :)