Self-Conflict

I am wondering why recently my self-esteem, self-confidence and self-value seem to drop down dramatically. It hurts me internally when i have to fall down from the top of a fruitful tree into a dry well of darkness. Some day, i feel on top of the world that i could achieve anything i want to. Some other days, i feel so blue that i don't wanna talk with anyone. I don't know whether this is called a cycle of life but i do know that life can be tough, and the more i grow, the more responsibilities i have.
I found myself easily trapped by the net of negativity. Those evil thoughts tend to hunt me every time i meet obstacles. Maybe i am a kind of guy who likes holding things to myself. The way i have grown is that I always do whatever it takes to help myself in the first step. I would not tell anybody that i need help. I tend to be strong but i am fragile and weak. I tend to smile but it is a fake one. I know there is something missing in my life. I wish i could be reborn to complete what is missing. Everyone has weakness and limitation, why should i care about mine? If i look at my pros, i have almost everything i desire at this time. I have a full family, a comfortable place to stay, a good job, a good school, enough money to spend, a nice car, a nice phone, a nice camera, a GPS, ipod, ihome, FM transmitter, a laptop with Internet connectivity, a person who loves me, etc. This is what i do when i am not happy: counting my property. What else do i need? I am never enough; i am greedy. We were born with nothing, why we desire so much? In Buddhism, one path to happiness is stay in the middle line. That's so true. If only i could detach myself from my ego, then i would not be trapped inside my self-conflict.
I don't know if what i am writing makes any sense to you because it is from deep down in my self-consciousness. I am writing this so that i could read it again, maybe in the next ten years, i would laugh at myself because i know that i am not controlling my mind, but the other way around.