What Causes A Dark Brown Discharge During Periods?

Hi 3 weeks ago my period was due and i started staining on the day my period was due which lasted a few days, a week later it started again as a dark brown to black dry blood which lasted a week but really only when i went to the toilet, which now has turned to bright red bleeding with clots,ive had tender breasts for the past month and are still sore which normally stop first day in period starts, is this normal as it has never happened to me before, im in my early 30 s