I gained 50 pounds with my daughter...............so believe in your Doctor. I am from the era that you should it for 2 but I think I ate for three thinking I was having twins.
Nanners is right on re the babies gaining weight...........so kick those worries to the curb sweetie and get rested up for those night time feedings that are on the horizon.
Congratulations on your soon to be family addition.
Hugs
Kitt