I'm not gaining weight no matter how much i try to eat. i'm 6 foot tall and around 69kg weight. i think that's why i sometimes feel tired?

3,500 kcal = 1 pound: Whether you want to gain or lose weight, remember that 1 pound = 3, 500 kcal. In other words, you have to have either 3, 500 kcal extra energy to gain 1 pound or 3, 500 kcal less energy to lose 1 pound. Try keeping track of every you eat & everything you. That should give you some idea of whether you're ahead or behind. Talk to nutritionist about what to eat. Mediterranean diet has good research.