cycle changes

I normally have a 26 day cycle but about 2 months back I had a 31 day cycle and there's been other times where I've had shorter or longer cycles but mostly I'm 26 day. well anyway I was supost to start today (day 26) but nothing, although when I woke up I thought I had started as it felt like I did, if that makes sense. I'm overweight and thought this would affect my cycles but it hasn't, is there a chance it's now interfering? is there any reasons my period could be late. I'm not expecting to find out if conceived as I was away from my so during my fertile window this month and last.