The length of the period makes no difference. If you had one, even 2 days worth, you are most likely not pregnant.
If your cycle is regular and your period came early, it could mean that you didn't ovulate this month and your uterine lining was full enough to shed...that is not a regular period just that the lining could not hold anymore blood so it had to give it all up.
Start tracking your ovulation from the day 1 of 1/1
at 8:37 AM on Jan. 4, 2011