Frequent urine infection. Kindly advice.

I'm from Hyderabad. Underwent c-sec 7 months ago. Since 2nd month of delivery, suffering severe urine infection once/twice a month. I noticed that I'm being infected after having intercourse. I was on several antibiotics like Norflox 400, Zanocin 200,Monurol granules,taxim-oz, one dose of mikacin,zocon-as kit,foloup 200,percin; Probiotics like uti kit,goe uti. Also other tabs urispas,urikind,citralka,hyocimax as well. Still nothing changed my condition. My urine culture n routine show nothing abnormal. Even USG abdomen and pelvis indicated nothing wrong. Still I have no solution to this problem. I would be grateful if someone could help me get out of this problem. I got copper t inserted in Oct 17. I thought infection is because of copper t. But, I had this problem even before having copper t placed. Kindly advice.