I had unprotected sex 3 weeks ago (9/6) when I was fertile and took plan b two days later (9/8). I was supposed to get my period last friday (9/20), but on wednesday of last week (9/18) I started getting a very light period (I always get heavy periods) that has continued to today (9/27) more than a week, my periods last 6 days. Is this a side effect of plan b? It's not listed as one on their website