Last week I went to the doctor for ah doctors appointment to get back on birth control again. I felt I could be pregnant by my period have not came on and the month is almost over come Friday. I told the doctor the last time I saw my period was on January 15,2008 so she adjusted ah pregnancy test and she told me it came out negative through blood and urine. At this moment I was happy to know this but. At the same time I'm wondering why the test is negative when I missed my period.. what's the cause of my missed period when I'm not pregnant?