What Causes Vaginal Spotting After Having Levonelle Pill?

I took a Lenovelle on the 7th of January, 2015 within 24 hours of having unprotected sex. I had just finished my period (that was delayed by a week) on the 5th of January. I started bleeding and lightly cramping today (11 January) with no warning. I had previously taken a Lenovelle on the 16th of November 2014 and have had two regular cycles since. Is this a typical side effect of the pill?