HOW?!

I just want to know how women barely gain any weight during pregnancy or not get any stretch marks. It seriously blows my mind!! I just read that a woman only gained 6 lbs throughout her pregnancy. That's crazy to me! I'm normally a very skinny girl with an awesome metabolism. I weighed 115 pre pregnancy and was very good about watching what I ate and had a set of workouts for each night on top of walking during the day. I'm 39 weeks and have gained 35 lbs 😑 I also used stretch mark prevention cream religiously but it did not work. Also ALL I drink is water. So I just don't understand how some women do it! Someone please inform me 😂 it's too late for me but I'm just really interested in what your diets or routines were!