This is the first step in your journey to overcome your identity crises and rebuild a sound one, one that can thrive with the changes of life. You can read more about identity crisis in this post: The ultimate guide to knowing yourself and building a healthy identity
Being certain and claiming that you know exactly who you are and what you want, is a handicap belief, that will limit you from being curious to learn more about yourself and develop a more spacious identity.
Doubting yourself can be fearful sometimes. If you embrace it, though, it will liberate you from the walls of certainty and offer you unlimited potential to grow and choose who you want to be.