What do you think it is?

In my 14 months ttc, I have NEVER had an early period. In my entire life of periods, I've never had an early period. Well, at least not by more than a couple of days. I BDed on cd13, 14 and 15. And a few days before that too. It is cd18 now, and AF isn't due for about another 8-10 days. This morning, I wiped and saw bright pink blood. It ended up lightly -medium flowing for about 6 hours. Mostly just when I wiped. Now, suddenly, I have been wiping for a couple of hours, and there is NOTHING.