I would just try to eat more fruits and veggies.
It's possible it's just a big baby however I think the body know what it needs to gain and as long as tests for more serious things come back negative I wouldn't worry.
I am 5'7 and granted I started out weighing more ( 172 ) I am up to 205lbs now at 39 weeks and my doctor thinks I should have gained more
Dont worry. My sister went from 120lbs to 175lbs. Dr.s sometime worry for no reason. If your doctor checks you for diabetes, thyroid, preclancia, exc you maybe further along, just because you have a large weight gain dont mean the baby is gonna be big. Simply maybe your eatting to much.