Help! My baby needs to gain weight!!

Hi everyone,

My baby will be 10 months in a week and he only weighs 15lbs 13oz. He had a doctors appointment yesterday and they advised that maybe I should supplement with with formula or pump and and keep track of how much milk he gets. She also advised that I feed him more solids throughout the day. Here comes the tricky part, he only eats around six spoonfuls of baby food then he’s against it. Being a ftm I don’t have any tricks up my sleeve. Has anyone went or is going through the same thing and could give some type of advice?