Overweight but struggling to eat enough

Hi there looking for advice. I've been doing FB on and off for a while now but keep failing as I'm struggling to eat enough? Years of bad habits mean my default setting is coffee all day and binge eating at night. Each time I start a fb program and use their vegan meal plan so I know what and roughly how much I should be eating, but then flounder as I'm so unused to eating enough in a regular pattern. Being overweight, every one assumes I eat too much but it's the opposite. Any suggestions for how to adapt as I keep stopping the workouts as I keep feeling too full and nauseas but don't want to give up again! I hope that makes sense and any suggestions would be greatly appreciated! Thanks xx