Eating for two

Ok guys I need help idk what to do bc I feel as if I’m always hungry and have to eat like every two hours and then I gain weight !!! So basically I feel like I’m eating for two !!! Help plz !!!!! I’m 21 weeks today !!! Am I hungry or is the baby and body just telling me I need to drink more water ? And does anyone else feel it’s harder to do things like go for a walk or take a bath bath or move around ? Don’t get me wrong I love being pregnant but it’s very different;) but oh so worth it in the end bc you get a beautiful little baby boy:)