Look into the mirror. Take in what you look like, and face it. When you accept the fact that that is just the way you look, THEN you can start to think of ways you could dress, and style your hair, that can help to flatter you. Ignoring it will not solve the problem. Everyone else around you can see you. Not looking at your reflection won't make you dissapear, you will only fail to realize how you actually look 24/7.
You can actually do many things from as small exercise of positive affirmation (regularly), being around confident people , solving small mathematical problem and step wise you can take yourself to next level. Confident cannot be build overnight. You must work your way out. "Start by doing what's necessary; then do what's possible; and suddenly you are doing the impossible."