I am 5' 10" and 185 lbs. Right now, I am a 14-16 and can also wear juniors clothes. I wouldn't worry about the size... a 12 would be stunning, but just concentrate on exercising and doing cardio. If you do somehting that'll make you stronger like a special sport or weight lifting, you'll probably start to look smaller, but weigh more. That's the best thing you can do because I used to be the same as you (kinda' a big pants size and weight not much... That's because you can handle more muccle on you) and now I'm improving.