Spotting or Period?

So about two weeks ago is when I had my last period, I shouldn't have it for another week an a half or so but for some reason I've been starting to bleed. I've been on birth control for about 3 months now and it just recently started happening. I'm not sure if it's spotting or my period coming early. It's more of a dark red, brownish blood and it's more than what I would expect spotting to look like. Help?