I understand why these feelings are making you anxious and upset. Unfortunately, I can’t provide a good evaluation on the basis of a letter. I do think what you describe is serious. If you haven’t shared how you are feeling with your parents, I strongly suggest that you show them your letter and this response.
I think you need to do two things. First, make an appointment with your doctor for a complete and thorough medical check. You are at an age when the body goes through enormous change. Believe it or not, it’s possible that the bad thoughts have a physical cause. There are a number of conditions that can lead people to be paranoid, anxious, and emotional. Do also talk to the doctor about your sleep pattern. Sometimes a sleep disorder causes emotional instability and strange thoughts.
If your doctor finds that you are healthy, then ask your parents to make an appointment for you to see a mental health professional for an evaluation. Be as honest as you can during your appointment. (You might also bring this correspondence with you as a way to get started.) We therapists can only be helpful when people really share their thoughts and feelings to the best of their ability.
Whether your feelings are medical or psychological (or both), you can be helped. This has already gone on for 2 or 3 years. That’s already too long. Please get the help you need and deserve.
I wish you well.