Thanks for your query.
UPT is 95% sensitive when it is done on 1st day of missed periods.
It is 99% sensitive when it is done on7th day of missed period.
So i suggest you to repeat UPT on 1 week after missed periods.
You can as well get a transvaginal ultrasound
right away for definitive diagnosis of pregnancy
Wish you good luck.
Hope this helps,