Dare to be different and learn to be lonely

My first thought would be perimenopause. My sister is dealing with that (she just turned 39) and it really makes her cycles weird. Then again, hers have always been weird, so there's that.

Diet can mess up your cycles, of course, but you have to make pretty drastic changes to make a difference. It doesn't sound to me like you're depriving yourself of nutrients, so I doubt that's the issue.

Then again, it could just be a fluke, but you know how regular you've been, historically speaking, so you know if there's a reason to worry. I can't think of anything life-threatening for which sudden irregular periods are a symptom, but the symptoms for ovarian cancer are so vague that a visit to your doctor wouldn't hurt, just to be safe.