Sure sounds like a period to me.Periods sometimes vary, even drastically from what you're used to. SO many variables can create a change: hormone fluctuations, changes in diet, rest, activiy or stress levels, growth changes, the works.
So long as you are up-to-date with your annual pelvic exam and STI screenings, I wouldn't sweat it.
The basic rule of thumb is that if periods are nusual for three months or more, schedule a new exam. But otherwise, there's usually no need to worry.