Hi Retrogal, I've had the same thing with my AF, it arrived on the 11th right on time, but ended on the 14th (I'm a 7 day girl myself too) and have just had blood tests done today, so I'm hoping I'll find out what is wrong when I get the results on wednesday.
Go to the doctors and get checked out, even if you come up all healthy at least you'll have made the effort to make sure that nothing is wrong

I hope you've found out already though