Ay, I feel you, ang stress ng waiting talaga, lalo na pag negative pero delayed pa rin. One of my mum friends had the same thing din after she stopped her pills, at parang it took her body a few months to regulate kasi the hormones were still settling. Since you've done multiple negative tests na, I'd really suggest going to your OB para ma-check kung ano talaga ang dahilan ng delay, could be stress, hormonal imbalance, or just your cycle readjusting from the pills. Fingers crossed na malalaman niyo agad ang cause, kaya mo yan!