Thanks for the query.
test negative on 5 th day of missed period suggests less likely you are pregnant.
However to rule out early pregnancy, i suggest you to get your blood tested for beta HCG.
If the titres are increasing, then there are chances of pregnancy.
At 6 weeks you can get your transvaginal ultrasound
to detect gestational sac
and fetal heart rate
Ultrasound wound be most confirmatory in detecting early pregnancy.
Hope this helps.