18 wks preg with second child. so far gained only 1 kg. is this normal? how much weight should i gain in the remaining wks in total?

Pregnancy Wt Gain: Pregnancy weight gain recommendations are based on how much you weigh going into the pregnancy. As a general rule if you are underweight, you should shoot to gain 28-40 pounds. If you enter the pregnancy at a normal weight then aim for25-35 pounds. Someone entering the pregnancy overweight may only want to gain 11-20 pounds.

Obstetrician: For the sake of your and your baby's health you should be under the care of a doctor, preferably an obstetrician.