I am 5'7 110 pounds I see a lot of ways to lose weight but none to gain weight . I would like to gain 15 pounds healthy weight that is. I am told a lot I look anorexic I use to think I wanted to be that skinny since at one time I weighed in over 200 pounds. I wear anywhere from a size 0 to a size 2 . I think at at least 15 pounds heavier I would loook healthier.

A good way of gaining some weight is to intake more calories, but do so by eating some healthy calories.

Snack on some nuts, peanut butter, avocadoes, and other foods that are high in calories. Also, do some mild weight lifting and strength training exercises to get muscle tone, as muscle has more density than fat does.

Eat more. Sounds stupid and simple, but you need to eat more. ISneeze nailed it though... more healthy but heavy foods. Nuts and pastas provide a lot of fat and carbs but are good for you all the same.'

Do less cardio and more strength related exercises. Replace 25% of your cardio with other exercises like toning (crunches) and weight training to try to put on a little muscle mass.

You can also look at weight gainer formulas from GNC etc. They are for body building but the idea is the same.