My Period Was 4 Days Early. It Was Extremely Light

My period was 4 days early. It was extremely light & lasted like 3 or 4 days & was bright red. (My normal period is really heavy & lasts 5 to 7 days.) After my period ended I started to spot on & off dark red / brownish colored blood. I have been extremely nauseous all the time since my "period" started. My period has been over for 3 days or so & I'm still having strong menstrual cramps. What is going on?