It depends on how much you weigh. But I will tell you that any number below 1200 is dangerous no matter what your weight is, and even if you're not pregnant. Even when I was dieting I never dipped below 1400 and lost loads of weight. Ironically if I ate less than 1400 I would stop losing weight. At 1200 the average body goes into starvation mode and slows down your metabolism thinking that you're trying to starve it so that it desperately holds on to its fat reserves. It's not healthy to short circuit your metabolism this way and could lead to problems later on. At the moment I'm aiming for 1800-2000.
You don't have to eat a lot of food to get your daily required nutrients. As long as you are eating fresh fruits and vegetables and getting in some complex carbohydrates you will be fine. Personally I need protein as well and get it from salmon, chicken, beef, pork, all very good for you.
If you're still having a hard time getting in all your calories there are a few foods that you can eat in small amounts that add good fats, loads of calories and are packed nutritionally.
1/2 cup peanuts = 400cal
1 avocado = 150cal
1tbsp olive oil = 119cal
1 slice whole wheat bread = 80-100cal
1/2 cup raisins = 260cal
1tbsp peanut butter - 85cal
cheese
dark chocolate
Juice
small banana = 100cal
All these can help you pack on some more healthy and much needed calories. Good luck and let us know how you're doing.