I'm 21 years old and 300 pounds. I have tried to lose weight and nothing is working. What can I do to get this weight off?

Surgery. If you've truly exhausted every conventional method, including medical supervision, then surgery is your next best option, especially if you have developed any significant underlying medical conditions such as diabetes or hypertension. In a qualified setting and an experienced surgeon and dedicated aftercare program, bariatric surgery is the single most effective tool to lose weight.
Several things. You need to estimate or measure your caloric needs and reduce your intake 300-500 cals from this. Low carb diets let you be more generous with calories. You should have a medical exam to rule out any unexpected condition such as thyroid. Excercise will help. If you can't control food intake-than appetite suppressants or even surgery become options.