My are tiny): when do you think they'll grow bigger?

Okk, so I'm 12 right, I have cup size 36B..:( I'm 5'3 and I'm 106.4 lbs...:/ am I fat for my age? And when will my s get biggger? Will they? :( I hate having tiny like I'm a cup size B but I always look flat and my bras fit me.