Spotting

So on the 31st I notice blood light pink on my toilet paper when I wipe so I said oh my Aunt Flo just got here so tampon in but then I notice yesterday I didn't have any blood in my tampon but spotting and this morning I notice no blood but spotting again, I took pregnancy the day I thought my period start and it was negative. I am just confused. Any ideas why I could be spotting???