What is your height and weight may be foodbur eating not enough for ur body u require good nutrition tongain healthy weight. Surely can help with 4-5 KGS weight gain in month

Avoid junk foods,add extra calories to your diet,have 4 to 5 meals rather than large 3...add protein rich foods and healthy fats to diet for e.g..egg white...add fibre rich foods like green leafy veggies,carrots,Apple, etc. Add green tea to your diet .you have to eat more foods high in amino acids,calcium, zinc, iron, copper and magnesium...do regular exercise without failure......consult dietitian they will do the needful.