How can I gain weight?

I'm an 18 yo male, 5'9" and 121 pounds. About 14 pounds "under" weight, which is unhealthy.
I've tried eating well (not over-eating), and eating a lot of potatoes, but I don't gain weight.
Any suggestions?

Don't use junk food, fast food, or greasy foods because of the high transfat content and saturated fat, which are bad for you. Instead try adding some of these to your everyday eatting!
Any omega 3 fatty acid cources like Tuna, salmon, Flax, walnuts. Poultry, nuts seeds, legumes, chickpeas, kidney beans, peanut butter, omelets, whole grain cereals, rice, pasta, granola, bagels and cornbread. Try veggies like, avocados, olives, potatoes, peas, corn, squash.
Fruits like, canned fruit in syrup, dried fruit and fruit nectars.
Use protein powder, and nutritional supplements like Ensure, or Instant breakfast powder you mix with milk, at each meal. Don't forget to take vitamins and minerals. Use milk instead of water in cereals, soups, sauces. Mix cookedchop meat, wheat germ, nuts, beans, or cheese in casseroles, pasta, and sidedishes. Add at least 300-350 calories to your normal daily intake, minimum!

Try protein Shakes eat a lot of protein foods like fish, nuts,& steak.

hi to gain weight jz have a pocket full of cash & go to any restaurant & jz eat wt you feel like eating & keep eating dn care for anyone jz keep eating specially kfc chicken & junk & dont stop eating potatoes keep eating & at home to keep eating & whenevr you want to eat c that you eat & eat your favourote dishes...& trust me I followed this...& in october 2006 I weighed 36kgs & nw I weigh 55kgs...can you beliuve it???so jz follow the advice bcum fat b healthy tak care
regards
tinchu

you need to eat pie its the only way!