Ahhh stress, hormonal changes, atau maybe implantation bleeding yang tak jadi develop, macam-macam je boleh cause spotting macam ni even without pregnancy. Honestly, kalau UPT negative tapi period still delayed dengan flek keluar, best thing is see your doctor to rule out anything else lah, sebab irregular bleeding + delay bukan perkara biasa for you. Don't overthink yet, tapi jangan jugak delay checkup ye, better safe than sorry!