You're underweight. You need some muscle and a little fat to keep your body in optimal shape. I don't sugar coat overweight truths and as a former anorexic I don't sugar coat underweight truths either: your body is not in good condition right now. I'm your height and I used to weigh less than you, I didn't think it mattered until I started losing hair and getting horrible bruises and receeding gums from malnutrition. Runway models die of cardiac arrest just like fatties do. There's a reason the BMI scale has a bottom limit.