Are there shortcuts for gaining weight (fat specifically); any certain foods which might help? i'm 19, bit over 4'9, 74 pounds, and low on iron.

See Dr., then eat...: If one is truly underweight (based on height, family background, and body type), a Dr. can evaluate for a hormonal, digestive, or other disorder. If no medical cause is found, then one can add weight by eating more calories of nutritious foods, while also doing weight-training to increase muscle. Proteins: egg white, chicken breast, salmon, ... Better fats: olive oil, peanuts, almonds, tofu, ....

Focus on muscle gain: First establish there are no metabolic issues like overactive thyroid or absorption problem like celiac disease. Find a provider who can help determine your basic metabolic rate and how many additional calories daily you need to get closer to 90 pounds. Focus on nutrient dense foods that provides lots of calories and do strength training exercise to gain muscle which weighs more than fat.