Had same problem once. When I was 14, my beloved grandma died. I cried a lot. From one of the best guys in the school, my grades gradually plummeted down. My parents were uncaring so I had to bottle it up.
And release in controlled manner. Writing diary and describing my experiences. Pondering about life and death and
even more of this. Honestly, I kept thinking until I felt I was done.
It costed me a bit of my sanity and emotions, as I had no help in other people, but now I feel okay.
On the other, brighter side: Hey! You keep thinking about life and death! How many kids think about life and death instead of pocket money, hamburgers and that cute someone from their class? You are special, and should feel being 'special' in positive way
Also: start working. Working hard for money or something. The more you and your mind will be busy with some work, the less time you will spend thinking.
