Why am my period late if I took ellaOne in an earlier cycle and the pregnancy tests are negative?

Hello, on August 16 (the 26th day of the cycle) I had secured sexual intercourse but just in case I took an ellaone tablet (for the 4th day of the 30th day of the cycle) (I know that it should be used in emergency cases and it was irresponsible on my part) I got menstruation on time (the cycle lasted 31 days, which is as much as usual). Menstruation, however, had a changed character because it was scanty and longer than usual, but I considered it as a result of taking a pill (the more that ellaone was taken after ovulation and menstruation still occurred) To be sure, I did a pregnancy test after 10 days and 27 days from the ratio of both negative. But this month I've been late for 3 days. And I wonder if this could be the result of taking the pill, and if there are still any chances that it could be caused by pregnancy? (I haven't had any sexual intercourse since).