What is the likelihood of pregnancy after taking emergency contraception, experiencing a light four-day bleed a week later, and subsequently missing the next menstrual period, with no further sexual intercourse?
Emergency contraception, such as levonorgestrel, is highly effective, and the light bleeding you experienced a week later is a very common side effect indicating the hormones are working. These hormones frequently disrupt your natural cycle, which easily explains your currently missed period. Since you have not had further intercourse, pregnancy is unlikely. However, to give yourself complete peace of mind, I recommend taking a simple home pregnancy test, which will be highly accurate by now.