implantation bleeding??

I've been spotting for almost a week on and off my period is supposed to start in 6 days and my periods have always been like clockwork I've never had an early period in my life. could I be pregnant? I'm tired all the time and have had nausea. i haven't had any breast tenderness. this spotting just started out of nowhere and I know it's probably too early for a test. can implantation bleeding last a week?