Ay, I understand kung bakit ka worried, sis! Since your PT came out negative and it's been almost 3 weeks na, better go see your OB para ma-check properly, sometimes may mga bagay na hindi pa visible sa home test, or baka may iba pang reason bakit delayed ang period mo like stress, hormonal changes, or thyroid stuff kaya talaga kailangan ng proper checkup. A few of us din nag-experience ng delayed period na hindi buntis in the end, pero doctor's visit talaga ang safest way to know for sure at para makuha mo peace of mind!