1. keeping in accordance with your height to weight ratio it seems that you are slightly having few kilos less than what is desired.
2. you are UPSET itself is one cause of not gaining weight, because in these cases metabolism
of a person is affected and increased leading to faster removal of food and reduced absorption.
3. or it can be due to inheritance,faulty food habits,increased physical activity with decreased energy(food) input, or if suffering from any problem related with digestion?
4. sometimes low hemoglobin
or worm in stomach is also the cause of not gaining weight,check your Hb% level and stool test
5. Mango shake is an ideal drink for you as one is free from protein (mango) and one is free from sugar (milk).
6. Don't let yourself stressed out, take diet rich in calcium (milk,curd), Vitamin D (milk,exposure to sun), magnesium
(green leafy vegetables).
7. do compound exercises,increase protein and complex carbohydrates in your diet, sleep a lot (which will conserve energy needed for awakening).
8. make sure you are gaining weight on muscles and not FAT,so apart from eating also follow a good weight lifting programme.