Mommy opinions

I am currently 21 almost 22 weeks pregnant and I went in for my gender ultrasound this past Wednesday. The doctor told me the baby is measuring really small for where I am. Nearly two weeks behind in growth. This worried me a lot... My sister and mom immediately put me on a high protein diet. But aren't worried about it at all. Being a first time mom this does concert  me I want my little one to grow healthy and strong. And I don't know what to do.