My last menstrual flow was from 9th november to 13th november. On 14th november I had sex with my partner. He used protection. But to exclude any chance I took unwanted 72 in 2 hrs. On 21st november suddenly it started bleeding. The flow was not heavy as period flow. And the blood was dark brown to dark red in colour. The flow continued till 23rd november. My original menstrual date was 5th december. From 4th december I am experiencing pain in my lower back. And from 5th or 6th december I am having sudden cramps in my abdominal area. But there is no period. I tested for pregnancy on 7th december and it was negative. Its been 4 days my periods are delayed. When would I get my periods? What should I do?