All sinners know they sin because God gave us each a conscience. Con = with, science = knowledge. The problem is no sinner can stop sinning on their own.

Don't worry about changing yourself drastically or anything. We're to rest in Jesus's finished work. Jesus said to come to Him if you're heavy-laden and weary, and that his yoke is easy and burden light. It's so much easier and you'll have peace. I hope you find it!