trying to recover from an eating diorder

I am trying to recover from an eating disorder. I can't really eat that much because my body isn't used to it but any little thing i do eat I notice that my weight goes up and my clothes fit tight. I know there is no possible way to put so much weight on from eating only a tiny bit but it's happening and it's very scary. I know that if I ate the amount of calories that it would take to maintain 105 lbs. my body would blow up. Is my body retaining water? What's going on?