Bleeding a week after period but 3 negative pregnancy tests?

I ended my period a week ago today, and yesterday I started bleeding again. I'm not sure if I'd call it spotting, but it's not enough for a tampon. I took 3 tests yesterday and they were all negative. I recently went through a breakup and have taken that very hard....not eating, stressing myself out all of the time, not sleeping too much, etc. Any ideas on what this could be?!