But yes if you are concerned about this then go to a doctor.
Being only 0.2 BMI underweight isn't a great concern. My BMI is 15.7, which is well underweight, but I eat a lot (eating four eclairs and 12 biscuits in a day as well as full meals is not uncommon for me) but I never gain any weight. However, I don't have any major health problem.
a bit underweight, but i wouldn't worry, i'm the same height and age and i'm 6 stones and a bit. that would be very underweight according to my bmi, but i do not have any problems at all and eat the same amount as the average person (maybe a bit more... ).