Early periods do not always mean pregnancy. For some women the early bleeding is implanation bleeding but this does not happen for all women, for instance I have not had it for my two pregnancies. For some women they are unreliable cycles and dont run on the every 28 days cycle. For some women it can be stress realted. For some women it can be a M/C. The only way to know if it is pregnancy is to take a test at least 2 weeks after the last time you had sex. Good Luck!!
I also started 10 days early, I have been moving and that brings along stress. Could I of been pregnant?
How long did the bleeding last and how heavy was it? If it was really light---didn't fill a whole pad or tampon--- and only last a few days it could have been implantation bleeding which is why the test would've been negative. I would test again when your "real" period is due.
Then again it could just be a freak cycle. Good luck, though