Help!!! I’m never late...

So I was supposed to start my period on 8/6. I am now two days late. The last time I had unprotected sex was on 7/31 which was a week before I was supposed to start. I have a 26 day cycle so I was well out of the ovulation phase and I made sure my partner didn’t cum in me. I think the chances of me being pregnant are pretty low so what could this be??