Emotional roller coaster

My life is like an emotional roller coaster,one minute I'm extremely happy or at some level of contentment and the next thing I know I'm at a depressed stage sometimes for apparently no reason. I'm getting frustrated with myself,I hate not knowing why I have all these emotions I mean where did they all come from. The emotions just hit me all at once from a smile to a frown.
I know right now I feel empty like something is missing in my life I really wish I knew what. Should n't I be the person to control my happiness,so why when I try something always seems to get in the way? School,sucky friendship,etc... School I know for sure is a key element in my rollercoaster cause quite frankly i feel like I'm on the brink of failure *sigh* that worries me really it does. This has been my worst semester so far& I can't wait for it to be over.
I constantly feel sick I wish I had some clue as to why. But still nothing is explaining why my emotions are so random and frequent, am I bipolar? :S I am seriously wondering that, am I schizophrenic sigh I really want some answers.
I hate what I'm feeling, I mean how can it be normal to love&hate a person all at once,one minute your at your happiest with them&the next u feel like u just want to strangle them or run a knife through their heart. When did I become such an emotional wreck...i used to be the girl who had some level of emotional stability, the girl who gave advice but now I'm the girl who needs advice, the one who needs to be comforted.
I fear that this emotional rollercoaster is going to cause me some of the most important people in my life, feel as if I'm going to end up hurting them or pushing them away.
I need an outlet, I need some way to let it all out,I need an escape&most of all I think I need to re-find myself. I want to be the girl I used to be just a bit stronger,I want to take control of my emotions again&just be happy.