I gave a lot of thought on this subject and I didn't really come to a conclusion, but I tend more to think that there is nothing after death.
I did have a theory once ... that death would be like an eternal sleep, with dreams and shit. If it would be so, "heaven" and "hell" could be explained as good dreams and nightmares, depending on your final mind state: if you are in peace with yourself you would probably enjoy your sleep, just as you do when you go to bed ... and if you have things that your conscience can't agree with, you would probably experience a nightmare, just like in real life when shit bothers you, you dream it. But the theory is absurd since after death there wouldn't be a functional brain to project your dream. It was a quite infantile theory, but I thought it would be ok to share it. Maybe others have or had other personal explanations in their teenage years even if they were wrong.