Hello, thanks for using health care magic You were on contraceptive pills before you had the unprotected intercourse and four days after the unprotected intercourse you took the EllaOne pill. EllaOne pill is a progesterone-like drug that is effective in preventing pregnancy up to five days after unprotected intercourse. Though the effectiveness is more during the first days, the fact that you were on contraceptive pills already makes it less likely that you could be pregnant. The delay in period is likely due to the effect of the EllaOne pill which causes an alteration in menstrual cycle such as delay, heavy menses etc but only for a couple of cycles. However, you still have to wait and do a pregnancy test later to be sure. Best regards and hope this helps you Dr Achuo