What Causes Abnormally Reduced Menstruation?

I am having a weird period. I was scheduled to start today 03/20. I have a normal 28 day cycle. Yesterday, I started seeing a brown discharge when I wipe myself and today I see red blood when I wipe myself. No flow like I usually have and a small amount. I took a pregnancy test yesterday and it was negative. What could be the problem? Could I still be pregnant?