What supplement can i take for lack of energy?

Depends: You need an evaluation to ascertain the cause of "lack of energy" as it is not a diagnosis, per se. It would be prudent to see a doctor for an evaluation. For 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.