What Causes Persistent Spotting Instead Of Periods?

hi i was supposed to get my period on the 12th and instead i got light brown spotting and had a lot of pregnancy signs, i went to a pregnancy center and took a test and it turned out negative along with 3 home pregnancy tests, a few days later it went back to normal and all the symptoms went away. then about 4 days ago the light brown spotting came back and is still happening. i was wondering what might be wrong?