What Causes Delay In Periods Despite Having Negative UPT?

I am 3 days late to my period, which typically will come early but rarely to never late that I can recall. I have been tracking my cycle for a year via a cell phone app and my average cycle is 28 days. I am 41 years old, I went to my OBGYN, and received a clean bill of health per se in regards to difficulty getting pregnant. I am OK with having another child, however I took a pregnancy test it came back negative. In particular I took this test on 1 day after a missed period and negative. I also normally get PMS symptoms ( moods swings and sore breasts). I seem to have no PMS symptoms this month. Maybe I am a bit more tired, but that is the normal, so nothing out of the ordinary that I can recall. I can recall many years ago in my late 20s, I tested negative but was actually pregnant, so I know its possible. However, I would think after 10 years pregnancy tests are more accurate and sensitive to the HGC hormone or perhaps my body has not produced enough. I don t seem to be an early menopause candidate, my mom is 60(still getting hot flashes) and it seem the average in our family is mid to late 50s. I am planning to wait until 1 week after my missed period or maybe my body just decided to skip a period?