How can I simmer my crazy emotions?

okay this is again another problem i have to face everytime, and its really bothering me at times. bah just read it, haha.
How can I stay more even-tempered at school, when I feel like my emotions are out of control! Or at least appear even-tempered and approachable! urghh!

I've always felt that I was good about being reasonable, assertive but not aggressive, pleasant, easy-going, etc, especially at at home and school (but mostly at school), (tapi pasal si iv selalu exagerate stuffs about us yatah cant simmer my emotions at most of the time, im sure the others tau pasal ani) but then, lately I feel like I magnify every small slight into something huge, that makes me snap at people and fume for days. I also feel like I'm going around with this general feeling that some people is against me (esp the girl who i have conflict with now) ( i know, i know. that's just probably what i am feeling)

I have a hard time just sounding pleasant and concerned, but instead accusatory & angry. I don't want people to start viewing me as a jerk or someone you have to walk on eggshells around. I also want to change my image from being a complacent slacker to being someone who is promotable (rather than someone who's too crazy & emotional to deal with people). - if you get what i mean.

How can I simmer my crazy emotions? I'm at the point where I feel like I am bitching about people too much (and their attitude, if it affects me), that I am incapable of having an adult discussion about my role without busting out into tears, and that being at a simmering boil all the time has made it so that people can literally see the steam rising from my ears! ( i just cant help this but yeah cant really control my emotions at times)

I'm like this at home too, but at least some people in this house has been understanding. I just really want to reign in my emotions so that I can think before I speak, not have a quavering or angry-sounding voice when I do speak, and try not to let people bother me.

Any suggestions? Tips? Books or resources?
help me, please? anyone?
thanks.