What can cause low energy and heavy breathing at age 26?

Need to examine: It is not feasible to provide a meaningful opinion without taking additional history, physical examination and may be some tests. It would be prudent to see your doctor and discuss if you may be depressed. Counter-intuitive as it may seem, exercise may help. Start with low intensity exercise such as walking and gradually increase the intensity at tolerated. Wish you good health! - Have a diet rich in fresh vegetables, fruits, whole grains, milk and milk products, nuts, beans, legumes, lentils and small amounts of lean meats. Avoid saturated fats. Drink enough water daily, so that your urine is mostly colorless. Exercise at least 150 minutes/week and increase the intensity of exercise gradually. Do not use tobacco, alcohol, weed or street drugs in any form. Practice safe sex, if you have sex. Get HPV vaccine

Plan: There are many reason. The first you have to check your sleeping habits, your activity and diet. If you sleeping enough, not overworking, have enough rest and exercise, eating regular food with variety of products, you should be fine. If still you feel too tired, you must go to the doctor and do some test, like blood work. Please, think it over.