If you think and talk sickness, fear, doubt and defeat as a child of God - YOU are what the bible refers to as "being conformed to this world". To be transformed in this world, YOU need to get your mind renewed with the Word of God and also learn to THINK, TALK and BELIEVE in line with God's Word.
You can not confess in your bedroom with your mouth that God will supply all your needs, the Lord is your Shepherd so I will not lack and walk down the street and the first thing that comes out of your mouth when your neighbor or friend asks how are you and you say 'things aren't going so well' 'I am down', I am depressed and feeling hopeless', 'I have too many problems' etc and expect your first confession to stand. YOU must learn to stick to your confession of faith both when you are alone, with friends and even at work. YOU must THINK, TALK and BELIEVE in line with God's word.
It is true that you live in this world and in this world there is worry, fear, doubt, anxieties, trouble, disease etc, however when these things do come, open your mouth and declare what God's word says about them and stick to God's word. The bible says "declare that thou mayest be justified", learn to THINK, TALK and BELIEVE in line with God's words.