I have a self-confidence issue?

You need to be upfront with her, as hard as it may seem, it's the best way. Sit her down and explain that you realize what has happened and you're a human being, you're supposed to change. Tell her how much it hurts you when she puts you down. You need to show her what it has done to your confidence and by her saying harsh things it's only making it worse. There are better ways of her telling you about what she thinks is a weight issue. She could say it in a nice way.