Brown spotting, negative pregnancy tests. What's going on?

I had sex probably 2 monthes ago.  I haven't gotten my period since then.  I started brown spotting pretty heavily 2 weeks ago, and I'm still spotting brown but it's gotten lighter.  One morning i had a lot of red blood, like i was starting my period, but by the next time i went to the bathrooom, it was light and brown again.  I've taken 3 pregnancy tests by Answer and all have come back negative.  What's going on?

[amberd5191]

Brown blood is old blood, have you every had problems with your period before? I would call a nurse line.