How Do You Gain Confidence?

I need some suggestions. I have never been confident and have very low self esteem, not just when it comes to my weight/body image, but with all aspects of my life. I know there is no quick fix for this and I know confidence has to come from within and not from how others see you. I am starting to feel really anxious and discouraged. I have this fear that even if I reach my goals I will never be satisfied with how I look. This really frightens me and is really discouraging.

I am standing in my brothers's wedding at the end of September. When I was fitted for the dress I was four months pregnant. I ordered a size larger than what fit then. I had hoped that when I tried it on after I had the baby (I am two weeks postpartum) that it would be a bit on the big side and it isn't. It does not look good at all and I am extremely self conscious in it. I am not sure how much weight I can lose before it needs to be altered and am really not comfortable with my post pregnancy body.

I do not want they way I feel in the dress to ruin my time at my brothers wedding. I want to be happy for him and his fiancé, but am afraid that this dress is going to make me want to hide. I know this sounds totally ridiculous by the way :)

So is there anything I can do, any tricks you know to boost confidence and self esteem. My husband said that if I feel more confident I will look better in the dress. I don't know if that is true. Any help is greatly appreciated.