Can Postinor 2 Cause Abnormal Bleeding During Periods?

My last normal menstrual bleeding was September 24, 2013. It is normally a 35 days cycle, 7 days with the first 3 days being heavy, 4th day moderate and the last 3 brownish black. I normally have severe pain on the first 2 days. No premenstrual cramping. On October 21, 2013, my period came (early), it was 7 days but throughout just brown discharge that was light throughout, no bright red blood i had premenstrual craming mild however for about 4 days prior to the brown discharge. It was no light that i didn't need pads or tampons, i could afford to just use panty- liners. In November it came on the 26th, it was the same as in October with light brown discharge only throughout. I am awaiting my period In December still which should be due this week if it is regular for this cycle. I have a history of taking 2 doses of Postinor 2 in one month, on the 15th and 19th of September, 2013. I have not had unprotected sex since then and use condoms as my means of protection. I am wondering if Postinor 2 can cause abnormal bleeding for so long, in my case 2 to 3 months? Or could this be a sign of pregnancy? I have no symptoms such as urinary frequency, bloating, breast tenderness, I feel just fine and normal.