hi,thanks for query.In a sexually active women ,missed period unless proved other wise means pregnancy
.As you have negative pregnancy test the chances of pregnancy are less.The test available today are very sensitive and can pick up pregnancy as early as 2-3 days after missed period.Please repeat the test and go for ultrasound
to see presence of any products inside uterus
.If the ultrasound is negative then you can go for some tablets which can lead to periods.
wishing you good health.