Can adrenal fatigue cause constant lightheadedness?

It can but: In your age group, it is more likely to be anemia, low blood pressure, or low blood sugar. Try eating more often, avoiding sweets which can make your sugar drop. Try to drink enough fluids to keep your urine a pale yellow color (if its clear, that's too dilute, drink less) and try to get more protein in your diet. If not better with that in a week or two, see your doctor.