What Causes Delay In Menstruation Other Than Pregnancy?

I'm 39 years old, I stopped taking birth control exactly 1 year ago. I started out having my menses from that point every 14 days then gradually went to 23 days. This last menstral was 28 days. I have not seen it after that, I'm 17 dayslate. I took a pregnancy test because it was the time I took a pregnancy test because it wad around the time of ovulation, both urine an blood test came up negative. I took the test when I was 14 days late. So is my cycle still trying to work itself out or what could it be?