Hey Love,

Weight gain during pregnancies varies from woman to woman, The average weight gain is between 10kgs-13kgs, but some women are different as i said before.
It could be also If you are excessively sick during the earlier months of pregnancy, you may find you do not put on any weight for a while (or possibly even lose weight). Usually when the nausea and/or vomiting settles, your appetite returns and you have a 'growth spurt' for a few weeks, as your body 'catches up'

could also be that some women retain more fluid than others. you could just be one of the lucky ones who doesnt retain much fluid.

Good luck