I should put on weight because i'm skinny, but i eat every kind of food, including fast food's. are there any relief?

Do not try to put on: Weight? If you are otherwise healthy, being skinny is not a disease. Soon enough you will start gaining weight and look back fondly at these days. Please eat a mixed diet rich in fresh vegetables, fruits, whole grains, nuts; low in saturated fats (that includes fast foods), no tobacco and no alcohol, exercise 30 minutes each.