Do I have a disease because God is trying to teach me a lesson and form me into His image?

No. God never tempts man with evil, neither is He tempted with it (James 1:13). Our enemy is Satan and he comes to kill, steal, and destroy. The Bible teaches that our lack of obedience to God’s Word—either because we don’t do what we know to do, or we are ignorant about what God has said in His Word—opens us up to the curse from the enemy (Hosea 4:6). God does not use disease to teach us a lesson! It is His goodness that leads us to repentance. (Romans 2:4)