What could cause a period to be extremely light with no clotting lasting less than 24 hrs two months in a row?

Light periods: The main reason for light periods is a change in hormone levels. Causes for what seems to be a light period can include: implantation bleeding in early pregnancy, thyroid problems, eating disorders, excessive exercise, initial periods for a girl, use of an intrauterine device, oral contraceptives & perimenopause.

Pregnant?: The obvious question-pregnant? If not, are you on the pill, any new medications, under unusual stress? The pill can cause very light periods. Give your doctor a call.