I understand your feelings.
It seems that your lean physique is bothering you too much. Since you don't want to take any supplements. But usually females gain weight after their marriage. Of you would like to wait for some more time it would be well and good. If you want to gain weight naturally than you need to take 2 bananas followed by a glass of milk and 2 bananas in the noon and 2 bananas followed by a glass of milk. Take diets rich in carbohydrates such as rice, oats. And you can take cheese, and all other dairy products. Increase the quantity of. Foods you're having now. And of it is not possible that way take limited amount of food but increase the meals no in a day upto 5-6 times. To gain weight it would take 3 months atleast by this way.