Weird period/possible TMI if you don't like the description of periods

So I'm on the pill and I know spotting is a side effect, but I started spotting dark, almost brown blood ten days ago while still taking the active pills. Three days later I started on the placebo pills but there was no change in the amount or colour. My period would normally be finished by now, but I'm still spotting!! Has anyone had this happen or know if I should see a doctor?