Pregnancy Weight Gain at 18 Weeks: Is It Normal?

Question
I am sixteen years old and i am now 18 weeks pregnant. As you probably have already guessed this is my first child and i have no idea of the things that are "supposed to happen". my family tries to advise me of these things but i just need some advice from someone else. I am just really concerned about the fact that i have not even gained a single kilo yet. i am only a small build person but every one else that is my size has already started to show at 18 weeks.    
please help me.

Answer
It could be that you aren' eatting enough or not eatting the right things.  If there was anything to really worry about your ob/gyn or physician would have told you.  Just make sure you are getting all the vitamins that you need.  Alot of women dont show until they are 5-6 months along so I don't think you really have anything to worry about.