I am teacher in high school and I see girls every day dreaming of looking like Carrie and Lady etc., but these girls can't. Why? Because they're not Carries or Ladys! They are Monicas and Michelles and Werwofs! We're all different and there's only so much we can do to our bodies, thanks to genetics.
I am 6'0, 180 lbs, which I am happy about. But my hairline is pointy and I have wrinkles around my eyes since I spend half my days laughing at my two kids. That's life. I have learned to deal with the things I can and the things I can't control At your age, it's tough to have perspective on some things since you're constantly being bombarded with the media telling you to do this or that. But if there is one thing you can control, it's how you treat your body and this is where exercise and diet comes in.
The benefits of taking care of your body go way deeper than how you look in a pair of jeans. The emotional benefits will last longer than both of these singer's careers. I feel sorry for someone like Lady Gaga, cause in ten years when she looks back at her 15 minutes (okay, 15 months or more!) of fame, she'll be begging for that kind of attention again while she's sticking botox in places it doesn't belong and starring in reality TV shows with the likes of Justin Beiber and "The SItuation".
(sorry, I digressed into teacher mode there for a second)
My point is, living a healthy lifestyle and experiencing the happiness that comes from this, is not influenced by one's fame or by the number of hits they get on Google in a week. You'll learn as you mature and begin to broaden your perspectives on life. I just hope you learn this lesson sooner than later.
Good luck, keep track of your progress, get a workout partner, cut down on the crap that goes in your body, and lose weight cause it'll make your healthier and happier, not because you hope to one day look good in a video with Beyonce and Tyrese.