I recommend you to read How to Be in Harmony with Yourself to get some tips for staying calm. You should know that working on yourself can be difficult and not an easy task.
It is important to begin trusting yourself. If you don't believe in yourself all your life, it won't happen in one moment. Remember that this article doesn't have a magical power.
This article has tips that you can immediately use, including writing about gratitude and finding reminders so you can be inspired in times of need.
Take the first step towards harmony, and then spend hours working to improve your self-esteem.