Depressed, Unhappy. Causing Headaches And Self Violence. Why Am I Frustrated?

basically for the past year i have been feeling very low. i can be very happy one day and in the same day start crying.other days ill be full of rage.i often have mixed feelings about my family which scares me , one day i really like them next day is like am plotting their deaths. am becoming really violent.in school am restless ,tired and try to get away from friends. for the past 3 or 4 months ive been cutting myself too. im really pissed also, because ive been having these BAD headaches for the past year and a bit.sometimes i feel like crying but i don t know why.my friends, teachers and family say that i look lost or confused. i tend to stare into space quiet often, in the most unusually times for example when crossing the road.i just feel really stressed and angry with myself as am writing this...