Late Period, 18 DPO, No Positive Pregnancy Test: What Could It Mean?

Question
Hi, I am 23 years old wiyth no children. I miscarried 1/1/06 and did not need a D&C. We have been trying again ever since. I have been charting my temperature and using OPK's. My leutal phase is always 13 days. My usual cycles are 28 days long. I ovulated late this cycle on day 19. I am now 18dpo with no sign of my period showing up. I am 5 days late, but have still not had a positive on a home pregnancy test. I am getting worried. Can I still be pregnant without getting a positive on an hpt? Could something be wrong? What else could cause a long Leutal Phase or a period to be late when I have ovulated? Any insight could be great. I'm calling my OB monday and see if I can get in and have a quantitative hgc test done. Thank you in advance for your help.
   -Amanda

Answer
If you you are now 18 days post ovulation,today,April 23, then you ovulated on April 6 (cycle day #19). The best time to take a pregnancy test is seven days after missing your next period. If you ovulated on cycle da #19, you were due for your next period on cycle day #32 (April 19) and should take a pregnancy test after April 26.  If it is still negative, you probably are not pregnant, but should take a blood test for pregnancy, Beta HCG, twice 48 hours apart. If there is a doubling of the results in 48 hours, it indicates a viable pregnany. If the value of both results is less than 5 you are definitely not pregnant.