16w- gained no weight

So at my last appointment about 5 days ago, my midwife and I realized that I have not gained a single pound and I'm 16w and I'm starting to bump out a little. I guess she's concerned because she's having me see a nutrition specialist this coming week to figure out why I'm not gaining weight. I'm eating normally (eat when I'm hungry, stop when I'm full kind of deal) and I eat pretty healthy for the most part. Have any other ladies experienced delayed weight gain? Is this normal? I'm only a little concerned becuase she's a little concerned so I figured I'd see if anyone else had this experience? Thanks in advance ❤