Hi, and thanks for your medical question on eHealth forum!
A light period lasting less than normal should raise the suspicion of pregnancy. Hence take a test and see. If pregnancy is ruled out, then scanty periods can be due to hypothyroidism, birth control pills, Cushing’s disease and disorders of adrenal gland, liver metabolism disorders affecting the levels of estrogen and progesterone and PCOD. Emotional stress and prolonged illness can be a cause too but unlikely in your case. It can also be due to pelvic inflammatory disease, infection (fungal or otherwise) and STD. Please consult a gynecologist to find the cause. Take care!