What Causes Irregularity In Periods, Brown And Grainy Discharge?

I am 45 years old and normally have a very short period. However, this month, my period started over 7 days ago, has not stopped (although it was and is extremely light), and the texture is brown and grainy. I also am now, after more than a week later, experiencing cramping and some bloating. What could this be? I am not overweight, have no known allergies, have had thyroid issues in the past (now controlled with meds), and I am sexually active (only with protection).