You aren't eating enough, which means you must have a really slow metabolism. I'm probably the same proportions as you, but I probably eat around 2,500 calories per day (although I exercise a lot). Because you're not eating enough, your body realises that it isn't getting the ideal amount of calories, and so it has become more "efficient", i.e. requires fewer calories to function. If you eat 4-6 small meals each day, amounting to 2,000 calories in total, and do some exercise, you will be able to raise your metabolism. I would recommend swimming twice a week for fitness, and weights twice a week to build muscle. Muscle will make you put on weight, but you will be slimmer because muscle is highly metabolic tissue, and the more muscle you have, the faster your body burns fat even when you are resting. If I were you I would ignore your weight and focus on your measurements instead. That way you won't freak out if you put on muscle weight, because presumably you're more concerned with your actual size than with numbers on a set of scales. You don't actually need to lose weight at all, but your lifestyle isn't healthy, and if you do want to lose weight, you're going completely the wrong way about it. Also, if you continue to eat so little, you will have weight problems in later life because as your body becomes more and more efficient, you will function on fewer and fewer calories, and will need to keep eating less and less just to stay the same weight. So weights really are the way forward. And don't worry, you won't get butch. Women just don't bulk up in the way that men do.