Hi , I am 16 very sexually active . And I didn't receive my period this month .I had sex on the 25th of march and I am now four days late for my period , This month . I went yesterday to the doctors , negative pregnancy test , but the days I was suppose to get my period I have been having very sensitive breast , bad cramps , back pain and nausea when in car . I tend to feel sick . I don't kno wat to think about confused , please help me . Thank you ! : ))