Menstrual bleeding last about 16-18 days?

I am going to the doc on the 30th but am wonder what would cause someone to bleed for that many days. It starts out as spotting for about 5 days then stops for a day then turns heavier all the way up to day 16. I am not on any medication. Nobody has ever heard of bleeding that long. I am 32 years old with one child. Im hoping it is not menopause early. please answer if you know what this is or know someone that had this and why.