What Causes Delay In Menstruation Other Than Pregnancy?

am i pregant ?. i am a healthy 23 year old girl. last period 23 august2010, i ovulated 1 1/2 weeks later. i am 17 days late according to my chart. i am spotting a little, and a little bit of cramping. im getting hunger pangs far to often this is unusal for me and i am very moody this last few weeks. and have a history of maicage. i have done 3 home pregnancy tests all negitive