Suggest Remedy For Brown Discharge And Cramping In The Vaginal Area

Hello, I am 33 years old and have always had regular menstral cycles, with normal bleeding. I had my last child 3 years ago and had my tubes tied during a c-section. About 5 months ago I started having 2 periods a month usually 16 days apart from each other. They always strart with a dark brown discharge and then I bleed so heavy I am having to change a pad every hour and half to two hours, and I also have very large clots with these. My bleeding last 5 days and ends with a brown discharge for a couple of days. Is this normal and what is the best over the counter medicine I could take to ease the cramping? Sometimes the cramping even goes down in the vaginal area.