How much weight on average are you supposed to gain by 20 weeks?

I know everyone’s bodies are different so I’m just looking for a range. I am close to 20 weeks and have gained 7 pounds. Two people have commented recently and it made me concerned. This is my first baby. One said “you are so small for 4 months.” The other said “only 7 pounds?” and indicated that I needed to gain more weight. I want to ensure my baby is growing at the rate they are supposed to.