irregular period or implantation bleeding ????

I had what I thought was my period for only 1 day 1/2 on Sunday but on Saturday I was spotting so I assumed It was  my period but it didn't last that long at all and was only heavy for a day. Then on Monday night it was totally gone and for two days I was spotting light pink / brown. I took a test it was negative but I'm gonna be taking another one next week.