Does Taking Postinor 2 Cause Spotting For Long Time?

Hi.... I had sex with my bf a day before my period. I was late for a week by then. He ejaculated in me and we were quite worried about me getting pregnant so he went to a pharmacy and got me Postinor 2. After taking it, my period arrived a few hours later. It's been about 16 days and there's still light bleeding. Its more like spotting and its brownish in colour. Smells like normal blood and I feel a bit itchy when it comes. Is this normal side effect of the medicine?