Terrified about gaining weight

My whole life I've been on the slimmer side and this is just what I'm used to. I was lucky to never really have to work hard at it and I was very comfortable in my own skin. While Im excited to be pregnant, I'm terrified about gaining weight. I'm not sure if terrified is the right word, but it feels like a part of me is slipping away. There are already so many things I feel like are out of my control: fatigue, changes in what I can eat, morning sickness... I just want to hold onto something of me. Anyone else battle this and have advice about how to kick this terrible feeling??