I had unprotected sex on 3rd april.. i have taken unwanted 72 in the evening of 4th of april.. after having i pill ... I have bleeded little for 2-3 days. After that we had again unprotected sex on 16th of april... My regular period cycle was 27th of the month... But till now.. my period is miss.. I have also urine pregnancy test on 30th of april.. but the test was negative.. Is there any need to worry? Why my periods are missing.. what can be the reason.