Hi, sometimes, gaining weight may not be easy, if by hereditary, you are of the “skinny body type” and one with fast metabolism. I will offer a few suggestions.Count the number of calories you eat normally and increase by about 500 calories. Keep at it for a few days and increase further more and you will notice weight gain. Probiotics contain good bacteria and help with digestion. And Prebiotics are nondigestible carbohydrates that act as food for probiotics. Probiotics are found in foods such as yogurt, while prebiotics are found in whole grains, bananas, onions, garlic, honey and artichokes. A combination of two in a healthy diet is beneficial. Try this. Regards.