Thanks for writing to HCM
Some females have irregular periods
and even in ladies having regular periods can have irregularity some times.so, don't worry about this.
You can repeat urine pregnancy
test after 4-5 days as it can be false negative in early pregnancy due to low HCG.
For confirmation,you can go for transvaginal ultrasound
as it is more sensitive in early pregnancy to see gestational sac