I have always been regular 32 day cycle then last month had a 45 day cycle so this can happen for what reason I am still not aware!! I suggest taking another test using morning urine however some people just dont show up as early as others so if u cant wait another few days book yourself into get a blood test this is the best way to find out it very may well be that you are late due to pregnancy or it could just be stress!! :) good luck I would love to hear how you go!
I agree with vmvnpv that it can be any number of reasons! Also, some people have a hard time with hpt's showing up positive. When I got pregnant with my daughter, I had one EPT test show positive but then I had 2 store brand tests and at test at the health department and my family dr show up negative. My dr had to do a blood test just to be sure I was pregnant. If you still haven't started your period, then I would talk to your doctore and see if they will do a blood test on you to check for the HCG level.
It can be any number of reasons. Late ovulation, no ovulation, stress or just a crazy cycle. Or you may have tested too early and the HPT didn't pick up on the HCG levels yet.