I know that the way it is worded isn't completely clear but the fact is, anytime you take plan b, it's going to cause some kind of impact on your period. Whether it's breakthrough bleeding, spotting, no period, a heavy periods, or anything in between, any of those can and do happen to someone who takes it.
If it were me, I wouldn't be worried about it at this time. Your next period will likely be different due to the plan b.