Hi thanks for your question.
Your having frequency of micturation and dysurea (burning sensation).your urine culture is sterile after 48 hours and routine urine examination shows 2 to 3 puss cell . You are on norfloxacin
.There is no relief to your symptoms from treatment.
Most probably your having cystitis
that is infection of urinary bladder
Continue you treatment for a week and meanwhile you can increase the PH of urine by alkalizing you urine with plenty of water intake and with alkalizer like disodium citrate.The increase in PH of urine will decrease burning sensation.
Hope this answers your question.