Most Helpful Guy
Based on what you typed, you are insecure about being skinny. This insecurity lowers your self esteem and prevents you from being confident. There's your answer right there.
Hardly any girls are going to turn you down just because you are skinny. They will if you are fat, so be glad you are not in that situation. You get overlooked or turned down because you are not comfortable in your own skin, and women can smell that.
The solution? Take your confidence back and embrace being skinny, or start lifting weights.