Dear , you may have infection
, stone in lower ureter, bladder outflow obstruction, anal fissure
due to constipation
or you may be drinking enough fluids. So start drinking a lot and see what happens. If not better then get urine test and look for infection and take antibiotic if so. Still not better or urine is normal then get usg done with full bladder volume, bladder wall thickness on full bladder, and post-void residual urine measurement. Post reports along with pictures of the scan here.