bleeding 12 days after period???

ive always had very heavy periods(ive had to have 2 transfusions because of heavy periods) i was diagnosed with pcos insulin resistant. ive been on metformin 750mg for about a month now and for the first time i had a period come on time july 31st and it very pretty light and stopping after 6 days. my highest ovulation days was the 16th and 17th of this month. i started spotting pinkish then brown on the 16th and i continued to spot. on the 20th it picked up more and but it still was pretty light but coming and going in spurts. i spot for an hour then go two or three hours with nothing, and some of the spotting would come out like a medium period but then would return to light. . today is day 7 of the spotting. what could this be? should i be concerned?