Not gaining enough weight 29 weeks

Hey there! My doctor wants me to get another ultrasound in two weeks because I haven’t gained weight. The first 16 weeks I was so sick I actually lost weight & now I have technically gained that back but from my last appt (4 weeks ago) to now I have not gained anything. They are considering that I haven’t gained any weight from my starting pregnancy weight bc of the weight loss. Any input or experience with this as well? They just want to make sure that he is growing okay and everything is healthy. I am not that worried currently but would still love to here anyone else with this experience and what you found out! Our extra ultrasound is in two weeks! Thank you!