Thanks for the query.
According your description the possibilities are:
Menstrual irregularities like hypomenorrhea
and delayed periods due to hormonal imbalance.
bleeding in the last month.
So as urine pregnancy test kits are less sensitive in detecting early pregnancy, you better go for blood test
for pregnancy to rule out the possibility.
If comes negative you once consult gynecologist and get evaluated for menstrual irregularity.