This also became an issue because I had to start thinking about what to study in college. But after a while, I realized, it would be very hard for me to decide a specific subject to study. So I turned my focus away from the subject, to what kind of person I want to be. Once I found who I wanted to be, I realized that it helped me in deciding what to do.
So don't worry too much about deciding your future, cause it will come in time!