What Causes Dark Vaginal Bleeding And Delayed Menstruation?

Hi I m worried I may be pregnant. I had unprotected sex 4th saterday and 5th Sunday, took the morning after pill on the 6th Monday, my ovulation date was the 7th Tuesday, but I ve got spotting on the 11th saterday but period isn t due till 21st Tuesday. I don t have regular periods but usually not this irregular. Could I be experiencing implantation bleeding. The bleeding is dark red and not alot of it but its not a light spotting ? Thanks