What Causes Constant Ringing Sound In The Ear?

Hi. For my whole life, (I m only 14, but still) I have heard a constant ringing sound. If I am at school or  if it is noisy it is not very loud, but if I am alone(especially at night) I hear it very loudly. I have insomnia, and I only starting thinking that the ringing might be why. Up until about a year ago, I thought that was just the sound the world makes. Now that I think about it, that is really kinda stupid. ( when I say the sound of the world, I dont mean the things in the world, I mean the earth itself). I have learned to tune it out most of the time, but lately I ve been thinking about it, so it is louder.  I need to know what is wrong or if I can treat it or something. My parents wont be much help. I have found out I had several other problems that I never knew was wrong, and have told them, but they never do anything about it, and I don t think they even believe. I just stop telling them now about my problems. I have brought this up several times, but they don t care. Please tell something I can do. I also want to know what is wrong!! Thanks.