Negative test but light pink spotting

St

So on Tuesday I went to the restroom and when I wiped and I saw pink which usually means it’s my period and heavy flow is about to start within a few hours. Put a tampon on took it out in the morning and saw dried up brown on the tip but no fresh blood, it’s Thursday and I wiped again and saw pink, tested negative this morning. My periods usually come strong and heavy, never spotting. Any idea what it could be?