What to do if I'm 20 years old and have always been 98-103 lbs and I really wanna gain weight is there anyway besides eating (because I do eat) to gain weigh?

Increase muscle mass. Eating calorie dense foods such as nuts, eggs, fatty fishes, dried prunes, lean red meats and avocado can help increase your daily calories, and lean proteins can support your body during weight bearing exercise to build muscle mass (muscle weighs more than fat).