What Could Be The Issue When I Have Delayed Periods While Being Sexually Active?

Hi, I had sex on the 7th of April, I was on 3 days into my period and still took contraceptive within 24 hours. had sex again on the 31st of april and took contraceptives within 24 hours. this is a week past my normal period and i havent seen my period, i took urine pregnancy test and it is negative. what might be wrong