Wa'alaikumassalam! Sis, I feel you, memang confusing kan when symptoms scream pregnant tapi UPT negative. A few of my mum friends actually experienced this, and honestly some took multiple tests or waited a few days baru dapat positive line. The thing is, UPT sensitivity varies and sometimes HCG hormone level tu tak cukup high lagi early on, especially kalau implantation baru terjadi. Since you're having all those symptoms (late period, headaches, backache, cramps), I'd really suggest you go see your doc for a blood test, it's way more accurate than UPT and boleh confirm faster, plus they can check for multiples straightaway if you are expecting. Jangan stress yourself lah, most cases turn out fine, just need proper confirmation first!