Need advices to gain weight

Any mummies face similar issue too? My spouse and I are quite petite, hence our babies are petite too. My first child was born slightly smaller than peers. When I was pregnant with my first child, if I'm 32 wks 2 days, first child by scan is 31wks. But this pregnancy, my second child is smaller. I'm 32 wks preg, but baby is only 30 wks. My bump looks like 4-5 months preg. I have been trying to eat more meals every few hours. But I'm not gaining enough weight. My last pregnancy I gained 16 kg, this pregnancy I only gained 4 kg, lost 8kg in first tri. Doctor say it's okay due to genes. But I'm worried. Mummies who faced similar issue, can you advise me what are some foods that I can eat so that my baby can gain weight faster? 😅 Thank you ❤️