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Most likely there is development of urinary tract infection
It usually occurs after unprotected sex and improper hygiene after it.
Drop of blood sometime comes during severe UTI
Go for cbc and urine test.
Start oral antibiotic like moxifloxacin
to subside infection.
Take nsaid to subside pain.
Drink more water and other liquids.
Take proper local care.Avoid sex till get complete cure.
Consult your family physician for proper medications.