Some people cant gain weight inspite of eating good food.. due to malabsorption,heredity or some other health conditions like worm infestation,vitamin deficiency..etc Need a proper diagnosis to advice you correctly.. Eat green leafy vegetables,eat citrus fruits,dry fruits,dairy products like paneer,tofu,cheese,eat more of pulses,legumes,soya beans,lentils,chicken,boiled eggs,meat,kale,sprouts,seasme and groundnut laddoo,ghee on daily basis ,more of water,divide meals in5 smaller portion..avoid eating in bulk,drink almond milk twice ,do physical activities,avoid tea coffee,more salt.. Eat more of milk products and sweets.. Go for protien supplements under doctors Guidance..