Hello doctor , i ve been skinny always . i am 19 and i just weigh 49kgs . i am a vegetarian . i eat more still i am not able to gain weight .

Increase calories: Calculate your total calorie intake. You will need to increase this above your current level to gain weight. You should also look at your protein sources and amount. With a vegetarian diet you will need multiple different protein sources to meet your needs.

Diet diary: Please keep a log of everything you eat for a week. Then discuss with your doctor. Often we are surprised but what we actually eat compared to what we think we eat.

See a physician: You nee full evaluation buy a trained and experienced physician in India. If you are otherwise healthy with normal appetite, eating balanced diet, normal periods you may not need to change any thing