What happened to Britney Spears voice?

If you go on youtube of young Britney or listen to her first few albums, you can hear her real voice is amazing! I love Britney, and I hate what the paparazzi have done to her. If you had millions of people watching you all day and crowds following you, talking lies about you, taking pictures, on top of that you have to manage your career and children, you would go crazy, too. You can say Britney wears such revealing clothes and a bad role model, but so is every other artist. I love all her songs, but one thing, why are her songs now so breathy kind of voice? That isn't her real voice, so what happened to it? Does she choose to sing in that breathy voice or what?