Losing weight during pregnancy

I am not gaining weight in 20weeks and my baby size is - 0.07 smaller than the minimum normal size, I think doctor will tell u if your baby size is normal or not, I am trying to chase the weight by drinking formula and some herbal, beside breakfast lunch and dinner, I also eat some snack about 2 hours after the meal, fruits, yogurt, cheese, on 22 weeks I gain about 2kgs and baby size is growing to chase the normal size, now still - 0.03 and I am still trying my best to keep eating to hope him growing well