Hi doctor. im 17 years old. my height is 167cm and my weight is 50-52kg. i know im under the average weight. what should i do to gain more weights?

Consider working wi: nutritionist and follow physician's guidance. Eat healthy high calorie foods. Eat 6 meals/day. Work on strength training to build large muscle groups. Workout w heavier weights w fewer repetitions. Sleep at least 8 to 9 hrs/night. Hydrate well w water.

Eat (more): Check out http://www.nhlbi.nih.gov/health/educational/lose_wt/BMI/bmi-m.htm which calculates your body mass index as 17.9-18.2 w/underweight being less than 18.5. 1st go see your family doc to be sure you're otherwise healthy. Serioiusly! Then check out http://www.mayoclinic.org/healthy-living/nutrition-and-healthy-eating/expert-answers/underweight/faq-20058429. Best wishes.