I have not had my period for 7 months now, and i've taken blood test and pregnancy tests and all were negative. i'm only 18 so what could be problem?

See you MD: There are many different reasons for missing a period like polycystic ovarian syndrome. Your md will ask about your history. Age , medical conditions like thyroid disease and diabetes, life stress, strenuous exercise, and eating disorders are a few things which can affect the menses. A blood pregnancy test may be considered.