No GD but baby is big

Hi mommies/ mommies to be, does anyone NOT have GD but baby is huge? I am 34w6d and baby is measuring 3.1 kg and opting for natural delivery. My gynae is confounded and advises me to control my weight and diet. I’m avg bmi pre pregnancy and have already put on 16kg. Eating less makes me feel v irritable and sad....