Not Enough Calories

I've been struggling with my weight for the past few months. I get full rather quickly, but I also don't eat the healthiest foods (mashed potatoes, bread, etc.) plus I snack a lot at work. I work at a restaurant and whenever they mess up a dish or if the presentation isn't good enough for it to be sold, its free game for the staff and it's hard to resists my cravings and the urge to snack. I also feel like I'm paying for my weight gain because my self-esteem and confidence is low as well as my energy. I've struggled with my weight my entire life and I was once 200 lbs. but then I started exercising and teaching myself healthier eating habits and I lost 70 lbs and maintained a weight of 135-140 lbs. for a good while, but I started gaining weight again when i moved in with my grandparents so I could go to school and I started gaining faster since I started waitressing and I've gained 20 lbs. within the last 8 months. What can I do? I also kinda have to be very "closer" about dieting because my younger sister is currently hospitalized for anorexia and I don't want my family to think I'm going down the same path.