I am 20 yrs old female with 41kg weight and 163cms. I appear to be thin and weak, but take the same food as my younger sister who is healthy with normal weight. My mother provides me with all the nutritious food, seasonal fruits and vegetables. But still I am not able to gain enough weight. I am a good student, and my parents are worried that this will effect my studies. I also have irregular periods. I have consulted a number of general physicians, who suggested me a liver checkup which came out to be normal. Every time I visit them, they prescribe me with some vitamin tablets and stuff, which don t seem to show any effect on me.Totally, am depressed about this and not able to concentrate. Please help me with an effective solution for my problem.