Very few women have a textbook 28 day cycle. Very few women have a cycle of exactly the same length each time. What happens is that the day on which your body ovulates can vary significantly from one month to the next. This then delays your period since the gap between ovulation and your next period (the "luteal phase") will usually be pretty much the same from one month to the next. If you ovulate a bit later than normal, your period will appear to be late. If I had to guess I would say that is what has happened to you this cycle.
thanks scary. tbh i am ususally 28 days but as you say it can vary. i did a pg test this am it its still brewing but showing a faint positive. I am not getting my hopes up as i bought a two pack and this is no.2 and the last one 2 days ago showed a bfn (unless I didnt wait long enough before I chucked it away - instructions, what are they for?) I think if I am not on in the next couple of days I might test with my super duper clearblue one. the silly one from my chemist has a silly plastic cage over where you pee and I dont pee straight so had trouble moistening it. we will see. off to check it again