What Causes Frequent Urination?

Hello, I am a 32 year old male.  I began experiencing frequent/urgent urination last week.  I have no other symptoms and have not experienced this before or had a history of any urologic conditions.  I went to a walk-in clinic earlier this week.  They checked my blood sugar level and it was normal.  I was told there were nitrites present in my urine, but the lab results were negative for bacteria.  I am currently taking cipro and was told to continue taking it after the lab results.   This is the third day on antibiotics.  I do still have frequent urination. They originally thought it was a UTI.  Should I be concerned that it might be something else?  Is there anything else I should be doing other than taking the medication?  Thank you for any advice.