Brown spotting- concerned! Advice appreciated

I apologize if this is TMI for some people. My period was due last week and it came maybe a day later than supposed to. I had taken a pregnancy test 2 to 3 days earlier and it was negative. When my period came the first day it was pretty heavy, but then got rather light and only lasted four days. Now after what seemed like two days of nothing, I have brown discharge/brown spotting to the point where I feel like I need to wear a tampon (although it doesn't feel completely right). Has anyone else experienced this? If so, what was the result or reasoning? Thank you for your help!