Have you tried speaking to anybody about
how you feel like a friend, your parents or a counsellor? Maybe it would help to get things out in the
open or off your chest at least. If you don't feel you can talk to anyone you could try writing things down in a journal or something?
Sometimes I find it hard to see things which make me happy, so I've started writing down one thing each day that made me smile/feel good, then you can look back at then, or just by coming up with stuff it helps. Sometimes it can be the most trivial thing in the world, like the sun is out or you watched a good film.
Maybe there is something in your past that is making you angry without you even knowing it?!
The caffine is probably contributing to the insomnia, maybe you should try some sort of meditation to get your thoughts to slow down and help you to sleep
"The Optimist sees the rose and not its thorns; the pessimist stares at the thorns, oblivious of the rose."
"Life isn't about waiting for the storm to pass, its about learning to dance in the rain"