1 Samuel 30:6 And David was greatly distressed for the people spake of stoning him because the soul of all the people was grieved, every man for his daughters; but David encouraged himself in the Lord his God.
When David found himself in a seemingly hopeless situation with no one to support him, he encouraged and strengthened himself in the Lord. Later on, that situation was totally turned around {see 1 Samuel 30:1-20}.
If you don't believe in yourself, who is going to? God believes in you, and it is a good thing too; otherwise, you might never make progress. You cannot always or even sometimes wait on someone else to come along and encourage you to be all you can be. Confidence is something you decide to have. You learn about God -- about His love, His ways, and His Word --- then ultimately you must decide whether you believe it or not. You will not go forward until you decide to believe in God and yourself.