Why do I feel so empty ?

I feel the exact same way. Everything that I've achieved and failed in was fueled by the desire to be "normal" and do what other people should be doing. Eventually, that feeling fades away and you're left with a hollow feeling. I'm still searching for purpose of life.

Sounds like you just need to find something new you really enjoy doing. Growing up, it is easy for us to 'think' that we are happy with the way things are, and we convince ourselves it's all good. If you really want a kick in the *** for motivation, join the Marines. Go be a Navy SEAL, or just get yourself in shape. Diet and exercise can totally transform you at your age (body and mind). Have you ever tried meditating? Holy Crap! Speaking of... do you do anything for spiritual health? Maybe tweak some things in that department.
I guess what I am saying is; paying attention to how we spend our time can help us understand what we need to stay balanced. We need to be healthy mentally, physically, spiritually, socially, etc. If we do not invest our time to cultivate the many areas of our life, we begin to notice that 'something' is missing. And try not to know so much. It's not healthy. The only thing you really need to know, is that 'you do not know anything at all'.

Most likely depression, I know because I have it. It started a year before I went into high school and I'm still depressed but slowly getting better. I've tried countless antidepressants but eventually stopped because they didnt work for me. But they might for you, try visiting your regular doctor and tell them this.

find a passion and immerse yourself in that. all i have is my music....i play and teach piano, guitar, ukulele. I also perform and write songs. Without it i'd be dead.

It is your own "FATE" that forces you to jump into such a wrong and hasty feeling.

Darkness at the break of noon, shadows even the silver spoon, the hand made blade the child's balloon, eclipses both the sun and moon, to understand you knew too soon there's no sense in trying.

All is samsara (chasing the wind)... check out a book from Anthony DeMello on spiritual enlightenment, that should clear this mess up for you. Good luck and god bless