I understand how frustrating it can be to feel like you can't control your own emotions. (I am like that when I have pre-mestural dysphoric disorder episodes....I get angry and pissed off at the stupidist things, and usually I'm a somewhat happy person.) One thing that has helped me is seeing a therapist. It helped me figure out why I am having the 'burts' of feelings I feel like are just pouring out of me.
Have you thought about talking to a therapist or maybe a close friend or family member?