Eh macam ada kemungkinan banyak lah, could be stress, hormonal imbalance, or timing yang off even though OPK positive (sometimes LH surge ada tapi ovulation tak jadi). A few of us dalam WhatsApp group ada yang delay pastu OPK positive tapi UPT negative, ternyata cycle mereka just off that month je. Best lo check with your doctor to rule out anything else, they can do blood test untuk confirm if ovulation happened or not, sebab OPK positive doesn't always mean pregnant ke or yang ovulated properly. Jangan stress sangat dulu, sometimes our body just decides to play tricks!