The strongest oak of the forest is not the one that is protected from the storm and hidden from the sun. It's the one that stands in the open where it is compelled to struggle for its existence against the winds and rains and the scorching sun
~Napoleon Hill~
Stop looking to others to solve problems for you, or to establish and develop your thoughts, your ideas, your beliefs. When you doubt yourself, you're not giving yourself a chance to experience confidence. No one can give it to you, and it's not something you don't have. It is inside you, it has always been there. Be willing to reach out to it. Changing your wording will help, but it takes repetition and conditioning on your part. Begin saying the opposite of what you've been saying: "I can't" turns into "I can" I won't" turns into "I will", and so on and so forth. Go within, reach in and pull out that confidence. Trust yourself, love yourself, believe in yourself, hug yourself and learn to rely on yourself.
When everything seems to be going against you, remember that the airplane takes off against the wind, not with it ~Henry Ford~