My doctor told me by second trimester the weight will slowly increase. If you can, get high calorie food like durians or potatoes or sweet potatoes to boost up the weight. I took durians (perfect excuse to gain weight), and baby's weight increased pretty quickly so I would say go easy on it. Avoid binge eating so that you have another excuse to eat again.
Do be caution too that if you have high risk for gestational diabetes, do consult your doctor.