I am 5ft2 and 18 weeks pg and very obviously pregnant.
I have a friend that started at the same height and weight (approx) and she is hardly showing.
I think it is not just your height etc that plays a part but also how you were 'designed' to carry a baby.
My Mum who is the same height as me but was smaller in weight when she first fell pg did excatly the same thing - i tend to carry loads of fluid and had 'deposits' where there never use to be, despite eating a healthy diets (hardly any extra intake of food) and plenty of exercise.
As someone that has got to this size early i am envious of those that hardly show. It can be very depressing at times!
HTH