Possibly pregnant?

  I am a 37 year old with a history of infertility (we have a test tube baby) but also got pregnant with my 2nd child with no help. My last period was July 1st.  I have always had irregular cycles, anywhere from 28-36 days, but have never missed a period except when I was pregnant.  I did a pregnancy test on day 41 and day 45 and both were negative, and now it's day 48 and I still haven't started my period.  I have no other symptoms of pregnancy.  Is it possible to still be pregnant, or is my lack of period probably caused by something else?  If so, then what? Should I be concerned?  
Dear Amy:
When a woman has been pregnant, her symptoms and sense of "do I feel pregnant?" is highly reliable. You express no symptoms of pregnancy and the tests have been negative. You likely are NOT pregnant.
Normal women are entitled to skip menstrual periods once in awhile. Usually, we have no explanation such as illness, travel across time zones, personal stresses such as job change, household move, weight change. There is increased likelihood that a woman will skip periods, randomly, as the years advance: age 35 forward begins the time when gynecologists expect women to develop more cycle irregularity.
If you do not start a menstrual period after 3 times your usual cycle interval (3 x 36 days) is the time when you should become concerned that something has changed.
Keywords: missed menstrual period
This information is provided for general education purposes only and is not a medical consultation. If you have specific questions, please contact your physician.