As a recovering anorexic why is it so hard to gain weight?

I've been anorexic most of my life and now that I'm recovering, I've noticed I've been gaining weight very slowly despite eating five to six times a day rather than just once or twice like I used to.
Update: I've also noticed since I've started eating, I'm starting to feel as if I can never get full, I eat and it feels like I never ate anything.
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