Hi...i am 19 years old my height is 5.5 my weight is 46 is this normal for me? But I want to gain weight so how can i? I am female

46 kilos. Your bmi is 17 which is just a bit below normal. I'd like to see you up to 48 kilos or so. Add more protein into your diet, extra chicken breast with meals, perhaps several protein shakes a day. Strength training is a good idea as well, to help you add lean muscle mass. Best of luck!