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Wow, it sounds like you've done a fabulous job of getting back in shape after having the baby! Most women would "kill" to only be a few pounds over their pre-baby weight so quickly.
I think it's just the depression talking. Lots of women look better with their hair a little bit darker in the winter, and go lighter in the summer when they're more tan. And remember, you didn't do this--the hairdresser did. I know that you know rationally that hair is easily fix-able.
As you get more focused on giving and getting unconditional love to your husband and baby, I think you'll be less critical of yourself and learn to love yourself more. I bet if your best female friend was being this critical of herself, you'd be telling her how great she looks, and what a good job she's done getting back in shape so soon after having the baby. So try to be as kind to yourself as you would be to your best friend--in a way, be your own best friend. The same way your husband can't feel good about himself if he's being criticized, you won't feel good about yourself while you're being so mean and critical to yourself. Be as kind to yourself as you would be to others, and this mental obsession about looks will begin to fade away.