Suggest Remedy For Delay In Periods

We have sex 15 18 days earlier without using a condom 7 days before when she test her pregnancy the pregnancy test shows that its negative but her periods have arrives till now she says that this is the first time when her periods gets late for 6 day Yesterday we have sex but this time the sperm gets in after 1 hours she take unwanted 72 By taking it she haven t got her periods till now.Dr. Please suggest the best for this .