What causes late periods?

My period is a week late. I’m always on a 26 day cycle. I only had sex one time in march and used a condom but it was on the day I ovulated. Any other momma’s have something like this happen and turn out preggo? There’s been no major changes\ stressors recently, just looking to see what the results of people in the same situation have been :blush: ( I’ll be picking up a test tomorrow)