Light brown, tacky discharge? Is something wrong?

Is this implantation bleeding? 
I started spotting light brown a few days ago with a couple dark brown clots here and there, and I have a week until my period starts. It's hardly enough to notice if you didn't look for it, but now I'm looking for it and it's starting to freak me out a little. 
Is it just old period blood? This has never happened before. 

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