Wondering if I should see the doc.

This is my first time posting but I'm in need of advice ASAP! I'm 27 and have always had a regular cycle, and occasionally have the normal dark blood spotting right before my pd. My period ended 12 days ago but yesterday evening I noticed I was bleeding, it is light pink and very thin. I assumed it was spotting which I know is common in other women. My concern is I filled half a tampon last night and am still bleeding today. I have mild cramping should I be concerned and go to the doc? I have just never had this much bleeding in between periods please help.