My period was due on 26th july. but now its 13th August (18 days late). I took the pregnancy test thrice at home and everytime it gave me a negavtive result, also i am having yellow vaginal discharge from the day i missed my periods ( i am not having any kind of itching or any vaginal infection). If the results are negative then what could be the reason that i missed my periods.

Also me and my partner had unprotected sex on regular basis which brings a though in my mind that i could be pregnant. But results are always negative. Should i totally rely on these results?? I am really confused. Please Help :(