I agree with Psychick, if you eat healthily and exercise throughout the pregnancy you shouldn't put on any more weight than is necessary.
If it is any consolation I am not a small girl even though I eat healthily and exercise regularly, the women in my family are big and I thought I would put on masses of weight really quickly, but as yet, touch wood, I haven't put any weight on and I am 11weeks along (I know there is still plenty of time for me to transform to biffa-woman).
Eat what feels right, don't deny yourself anything you want as it is not just you who is being deprived but your little one is too! Well that's what I keep telling myself.
Enjoy your pregnancy and use it as an excuse to be good to your body x