i am trying to exercise, but it's not going so well. I weigh only 119 pounds at age 20. That may have to do with the fact that I have always been underweight for my age--my birthweight was 2 pounds, 4 ounces!
What sort of exercises and foods would bulk me up? There's tons of stuff out there about weight loss, but I have the opposite problem. It's very discouraging to go to the gym, and despite my best efforts and desire to lift as much as I can, everybody else there is stronger than I am and seems to have gotten results. My lack of results discourages me, but it might be my fault since I don't think I work out enough, nor is there anyone there to tell me what or how to do things. So I could be doing everything wrong without even knowing it.
I was also born as light as a feather and have remained underweight my entire life, so I understand your frustration. I've been a little under the weather lately and my weight plummeted to 101 pounds.
I think our ages and your gender are significant contributing factors. My boyfriend is four years older, but we both had our most substantial growth spurts at the same time. Guys continue to gain height and to fill out into their 20s. In his teens you could count his ribs when his shirt was off, and now that he's in his 20s he's slowly begun to gain weight and have broader shoulders. So try to retain some hope that time itself will give you a boost.
Have you ever seen an endocrinologist and had your thyroid levels checked to make sure yours isn't overactive? Hyperthyroidism can contribute to being thin, and it's treatable. It's one of the reasons I'm so thin.
My nutritionist recommended that I eat high-carb foods that have more nutritional value, like brown rice, wheat pasta, whole grain bread (preferably ones like Ezekiel 4:9 that are complete proteins), yams, sweet potatoes, potatoes, granola, and steel cut oatmeal. These can all can be "bases" for other foods like stir-fries, sandwiches, casseroles, jacket potatoes, or parfaits. I used to be a vegan and returning dairy to my diet has made a difference. I have whole fat milk and whole fat yogurt now. It's also helped me to get in more protein. Fairlife's whole milk has 13 grams of protein per cup, and Fage's yogurt has 23 grams per cup. You can use the milk and yogurt for shakes and smoothies, and there are so many variations that can be tried. My stepdad makes this amazing date shake for me that has whole fat milk, cashew nut butter, walnuts, vanilla beans, cinnamon, and like a cup of dates or something. Dates are surprisingly caloric. A bonus to them is that they are so portable so you can bring them with you in a little bag and have it while hiking or whatever. Tropical fruits like mango, bananas, papaya, and pineapple will help you to gain weight more than berries. You can add them to smoothies, top yogurt with them, throw them in the juicer, or just have them raw. Nut butters are great for weight gain (not just peanut butter but also almond butter, cashew butter, walnut butter), and you can add them to a variety of dishes. Nuts are great, too. Avocados are fattening but healthy. I love avocado toast. Drizzle olive oil over it to add in more calories and fat. Cheese is also fattening but has protein. Get the kind that isn't processed. Juice doesn't have a lot of fat but it packs in calories. It's best to have fresh juice when possible.
MyFitnessPal is a free and simple to use app that tracks your calories, fat, protein, and carbs. Setting an alarm on your phone to remind you to eat might help. Eating something every three hours can be beneficial, even if it's just a small snack.
FitBit might help you to track the calories you've burned. If you're running, swimming, or doing anything else that burns up a lot of calories you might want to cut back temporarily. I was advised to minimize my aerobic activity to just 20 minutes three to five times a week for now. I don't think I can actually do that, but I might try. That's a dramatic decrease from what I'm accustomed to as a dancer and runner. Yoga is a way of stretchy and being active without really burning that many calories. Put more emphasis on strength training than aerobics for now.
As far as supplements and the like go, they've kinda sucked for me. I tried the Optimum Nutrition Serious Mass and the Pro Gainer protein powder and was underwhelmed with both. You might like them, though.
The Mayo Clinic has some good tips for gaining weight:
http://www.mayoclinic.org/healthy-l...ating/expert-answers/underweight/faq-20058429
Best wishes!