Aiyo, symptoms macam tu memang boleh confusing! Tapi honestly, brown spotting sebelum period dan negative UPT biasanya means period coming je, sometimes our body throws these curveballs, a few of my mum friends pun experienced exactly this, sakit perut, sakit pinggang, mual, everything lagi before their period showed up. Since your period is expected on the 21st, maybe tunggu a few more days and test again if it doesn't come, tapi kalau worried sangat or symptoms terus nagging you, better call your doctor to check properly okay, just to be sure everything's fine.