It's hard for me to consume enough calories too.
The trick for me is to plan my meals. If I know I'm having a 400 calorie dinner, then I make sure my lunch is going to be 700 + calories. That sounds like a lot of calories for lunch, but it's not if you have energy dense items...such as nut butters, olive oil, other condiments/spreads, pasta, sandwiches, bananas, avocados, beans, caloric liquids, granola, nuts, etc.
Here's some suggestions to boost up your current intake without eating junk food:
Breakfast: Yogurt parfait, consisting of: 1 cup yogurt (i'll average this out to about 200 calories - could be more or less), 1/2 cup granola, 1/4 cup nuts, 2 tbsps wheat germ, half a large banana ~ 700 calories
Lunch: Salad, consisting of 1 serving lettuce, 1 cup chickpeas, tomato slices/mushrooms/whatever vegetable you want, 1/4 a large avocado, 1 piece of baked marinated tofu, 1 serving of croutons (or 1 oz of cheese/soy cheese), 1/4 cup light salad dressing (I'll average this as 100 calories)~ 500 calories
Dinner: Same as lunch, but instead of the avocado, use 1/8 cup of pumpkin seeds. ~ 500 calories
Total: 1700 calories (of healthy food). With this plan, you are getting:
*iron/protein (chickpeas, nuts, seeds, tofu)
*calcium (yogurt, cheese, vegetables, fruit)
*healthy fats (avocados, nuts, seeds, chickpeas, granola, salad dressing)
*carbs (croutons, nuts/seeds, granola, avocado, banana, salad dressing, chickpeas)
*fiber (wheat germ, nuts, seeds, chickpeas, fruit and vegetables)