It could be DID. But a letter isn’t the way to find out. It’s long past time to see a mental health professional who specializes in trauma. You went through a terrible ordeal as a child. You may have done what many kids in that situation do — protected yourself by “going away” in your mind. It’s really a marvelous phenomenon. The mind can protect a child by creating an imaginary someone else to suffer the pain. But at some point, it’s important to put the self back together. I think you could interpret your current distress as your inner self telling you that you are now strong enough to manage the pain and work it through. You need to find a therapist who works with teens and who has experience with DID.
There are actually many therapeutic methods for helping people in your situation. One possibility is a technique called EMDR (Eye Movement Desensitization and Reprocessing). EMDR can provide a safe structure to help you metabolize what happened to you and get past your past. Ask your doctor for a referral to a local therapist, or search on the Internet.
You’ve suffered too long already. You know it isn’t going to get better without some help. Please listen to your own heart and get the help you need.
I wish you well.