weird period

I am someone who does not have an overly regular period, it's normal for me to miss a few months between periods. The date when my period usually starts (when I get it) was coming up and I had some cramping and slightly tend boobs. The day my period usually starts came and I started to have brown discharge, I thought it was weird but assumed my period would probably start later that day or the next. My period never really came, I had brown discharge and the occasional spots of red blood but that was it. I'm on day 4 of it and I still have brown discharge but always just a little bit on my pad. Does anyone have any idea what could be happening? I have never had anything like this happen before. I took a pregnancy test this morning just to make sure and it was negative. Any thoughts would help, thanks!