Aiyoh, I feel for you lah, yang sakit-sakit bawah perut tapi test negatif memang confusing dan stressful! A few of my mum friends went through something similar, and honestly macam-macam boleh happen, bisa hormones yang sedang keluar, stress (kerja pressure ka?), or something else yang kena check dengan doctor. Dengan cycle mu yang dah irregular 2 bulan ni and now 51 days, definitely worth seeing a GP or gynae to rule things out, terutama since ada pain; bukan nak scare-scare but better safe than sorry kan. Jangan lama-lama tunggu, go soon so you can get proper answers and feel better!