Bladder is not fully emptied. Anyone!

I'm 36 yrs with no BP,no diabetes,no smoking and no alchohol. Had used prolonged antibiotics( nearly 9 months of antibiotics over the period of 5 years) in treating for fistula in ano. I stopped using some of them as I get pain while passing urine. Fistula has been operated once again recently a month ago. From the last 8 months or so I'm having feeling of incomplete of passing urine. Means while passing it won't pass all at time will stop at the end and again have to pass it 2 or 3 times to completely empty the bladder. I get that situation whenever I am having the pain with that fistula/abscesses. Though it is operated with no pain, I'm getting that feeling again. What's the problem plz explain anyone Thanks.