According to the Bible "Therefore if anyone is in Christ, he is a new creation;old things have passed away , behold all things have become new. 2 Corinthians 5:17. It takes faith to believe this. Often times we doubt ourselves and if others tell us we need to know their truth or that we are not yet a Christian or others call us condescending names, then doubt could really come in or enter in.
What do we do when we doubt by listening to ourselves and others ? First we pray and study the Word of God , the Bible. Prayer and study of the Word of God should lead us deeply to who we are in Christ.
I believe it is like climbing mountain, it gets harder as we go higher but when we overcome our doubt or doubts we get stronger. So let us get to know who we are in Christ.
Yes we are a new creation, the Spirit of Christ and the Holy Spirit is in us.Feed on the Word of God and our inner man will get stronger.