My period comes every 26-28 days and lasts 5 days. But, I bled red blood for four days and now have been having dark blood...like almost black for 3 days. Making my period last 7 days so far. I felt great on day 5 and thought my period was leaving. But once this dark blood started my back started to ache really bad and I have cramps all over again : / tommorow will be day 8 if it continues. Is this normal?