Underweight baby during pregnancy

Hey everyone quick question I am 24weeks I will be 25 on Friday. I went to my ultrasound visit yesterday and everything was fine. The only thing the dr was a little concerned with is that th maybe is a little off on her growth for me being as far as I am. He said by a little and wants to monitor me and see me and four weeks for another ultrasound to make sure she's growing and gaining weight. This worries me a bit. I would like to know if there's anything I can do to help that as far as what I'm eating making sure I consume milk which I won't lie I'm slacking on. I'm overweight and my pregnancy has been pretty good I thought because ill gain maybe two or three pounds hit then by the end of the week I'll loose it and go back to the same weight I started when I first got prego. Any advice I would greatly appreciate it