I’m very surprised that your parents or teachers didn’t address this with you long ago. What may have started as a little anxiety has now become a much harder to break long time habit. The longer we are silent, the harder it is to speak.
One of the important developmental tasks of the teen years is finding your own “voice”. That means more than the act of speaking. It also means finding out what’s important to you and learning how to express yourself to others. Conversations are one way that we all clarify our thinking, refine our interests, and learn who we want to have as friends and, eventually, what kind of person we want to have as a partner. This is important stuff. You don’t want to miss out on it.
I encourage you to make an appointment with a counselor. In the safety of a counselor’s office, you can start to deal with the anxiety that is at the root of the problem and start to break the silence habit. You don’t need to become a “chatty cathy” to be okay. But you do need to become more comfortable expressing your thoughts and feelings. I really believe you have much more to say than you think you do.
I wish you well.