Missed my period for about a week. Negative pregnancy test , back ache and when pee , i wipe there's some brown sticky discharge and i thought its my period so i put a pad , usually menses it will stain my pad but this time round after so many hours nothing on pad so what could it be ?

Like the comment above, it could be implantation bleeding which can happen about 1 wk from the time of ovulation. If u have been tracking then u would know when is ur ovulation because for some people not every month's ovulation is the same time and sometimes there is and sometimes there isn't ovulation for the month. The human body is dynamic. Sometimes if ur are under big stress physically (sudden diet or a heavy session of exercise, or pple w Low fat mass) or emotionally (many), it can delay the onset or even cut short ur period suddenly. So the best thing to do si to observe. If 1-2 days still no menses, after another week check for pregnancy. If no menses, not pregnant, u don't feel unwell, u can just let it be. Observe for another 1-2 on the if this kind of weird menses experience occur again. If it does then you should seek medical attention