Not gaining weight during pregnancy

Hi mummies. I've not gained any weight since my first trimester and am currently at 18 weeks. I am overweight but have low appetite and morning sickness until now. Baby seems to be growing well for gestation age according to the scans when I go for appointment. But I'm wondering will baby continue to grow well if I still don't gain weight? Any mummies out there in a similar situation? Any response will be much appreciated, thank you.