What Causes Abdominal Cramps With Dark Red Clots?

I usually start my period every 29 to 30 days.. Its always on time and last abot 4 days. Last month it was 7 days early and this month I have not had it, I have been having brown discharge for 8days now only when I wipe and yesterday woke up to cramping and gooey dark red stuff coming out. I have not been on any birth control for years and me and my husband never use protection. Please help