period question

Li
Hi 
I wanted to get some input. This is the first time this has happened. I was due to start my period 4 days ago. Before I went to bed I used the bathroom , I wiped and seen alittle blood, sad face. I put a tampon in and the next 3 days I just had aliltlte brown blood. No period blood at all. I took a pregnancy test and its negative. Has anyone experienced this. What could it mean? Thanks in advance for your help