Missed period & negative pregnancy test
I am not on the pill, but my period pretty much comes every 28 days. I should have gotten my period this past Friday and now it is Tuesday and still no period. I was so worried I took a pregnancy test last night and it was negative. I read the instructions several times so I think I did it correctly. I am currently training for a marathon (I have done 17 in the past) so I am aware heavy exercise can delay a period, but this seems really delayed. How much longer should I wait for my period to show up before taking another test? I am 40 years old and NOT trying to get pregnant. We use condoms always so I am praying I am just delayed due to the heavy training.
Thank you