How do i gain weight?Even at d age of 24 I weigh only 38.?

Though i have good eating habit's,i mean I eat a lot, still I don't gain weight. I hv tried n numbers of tonics n medicines but they are not working out. Please help me out with this, I will be grateful to all of you. And i would like to mention that I dont eat junk much, but i have good quantity of home-made food.