One reason I wanted to reprint your letter is because I hope it will warn someone else who may be in danger of going down the same path you've followed. Drug addiction (whatever its cause) is a terrible and destructive thing -- as you are discovering.
You face a serious problem, and I'm very thankful you realize it and want to find a solution. The first step is to face the fact that you can't stay on the path you're on. Not only is it illegal but it's also destructive -- physically, emotionally, socially and spiritually. And God doesn't want to see you destroy yourself. He loves you and wants what is best for you -- now, and for the rest of your life.
This is why I urge you to turn to God and ask Him to help you confront this problem. By faith confess your sins to Jesus Christ, and ask Him to come into your life and help you. The Bible says, "God is our refuge and strength, an ever-present help in trouble" (Psalm 46:1).
Then ask Him to give you the courage to take the next step. It won't be easy, but go to a doctor you trust and tell him what's happened. He's probably dealt with similar cases, and can refer you to a pain clinic or other resource to help you cope with your pain. Don't give up; God is more concerned about you than you are, and He is always with you.