Menstruation is late

Never in my whole life my AF was late or I did not have cramps. Usually I get cramps before I get my stuff five days prior. This month I had one day where I cramped, that's it, and my menstruation is late. I never been late.. I didn't do a test yet.. But I'm sure I'm not pregnant... Does anyone else know what it could be? I had the last weeks pain on my left ovaty during sex..