Plan b question

So my boyfriend came in me and I took plan b I’ve taken plan b in the past before but this time I took the pill I got my period a week or so after now today was my original due date for my period to start & I’m slightly bleeding? I have brownish/pinkish discharge it’s not a full on period but every time I wipe I see it & I have painful cramps. Has this happened to anyone? I’m only asking because this is new to me and yes I tried to search it on the internet before coming on to here but I’m curios to know if any women have gone through this before & what it means, thanks