Unusual flow???

So about a week ago my fiance (an over the road trucker) came home and naturally we kinda threw caution to the wind and made love despite not having any condoms. He came in me (a mutual decision) and we did exactly that again in the morning. I took the morning after pill (plan B) and because i took it less than 24hrs from the first time we did it i just forgot about it. Well now yesterday i started cramping and spotting. But it's not normal blood it's a light to dark brown (like old blood) and it's feaking me out because my period isn't due for another 2 weeks. My period usually comes like clockwork. Does anyone have any suggestions as to what's going on???