Eh, I feel you lah, sangat scary bila period tak datang lama-lama! A few of my mum friends jugak ada yang mengalami ni after giving birth, especially kalau on hormonal pills macam Noriday, sometimes the body ambil masa lama to regulate balik. Since you dah test negative dan dah 3 bulan tak period, I think best you go see your gynae or doctor to rule out anything, bisa jadi hormonal imbalance ke, or the pill might not suit you. Jangan worry dulu, tapi check with doctor is really the best move so you can get proper investigation dan peace of mind, sayang.