I actually had some very long cycles like that for a
period of a little over a year (
period every 3 months) due
to a
slow thyroid. Have you had anything like subtle weight gain, dry skin, melasma (dark spots appearing on the face), little bit of depression???? all of these are symptoms I had, I'm sad to say. This was several years ago and it did self correct for me.
At this point, I'd go to your doctor, take a blood pregnancy test and talk to him about why you are this late.