Effects of plan b

So I have taken a plan b pill for the last like four months. Out of paranoia. This is the first month I haven't taken one and now I'm almost a week late. However, I always thought I was a 28day cycle but looking back for the last couple months where I have taken the pill I have started on the 23. Could the pill have just been making me early and now because I didn't take one I am on my normal 28 day cycle? If that's the case I would be due to start today or tomorrow. Not a week ago.