My height is 5 foot and 8 inch but weight is 45 kg. I am trying lifting some weight and increase appetite. But my weight is constant so what should I do?

See answer. You must first of all look at your family history. Then a medical evaluation is necessary. You may just have a good metabism. You are very young. Your exercise is good for everyone should exercise. Remember you do want to stay fit. If all you lab evaluation us ml just work on healthy diet and your exercise a normal lifestyle. Let your body take care of the rest.