not eating enough?

my midwife told me my last visit that i have only gained 3lbs and im 28 weeks.. she said she wants to see about a pound a week from this point on. i told my fiance about it and he told me that its because im not eating enough. i told him i eat regularly but he said the problem is is that my meals are in such small quantities. prior to pregnancy, i strugged with an eating disorder. could this be why my meals are still very small? how can i eat bigger meals or more times a day when im not hungry? this is really hard for me. please dont judge