hello,thank u for posting query.u have to strain which is indicative of either lower urinary tract
obstruction or urinary bladder
weakness.that causes urine stasis in bladder leading to recurrent uti.another reason could be prostatitis
may be allergic in your case as u are not getting any bacteria in urine.u need to undergo investigations in form of usg kub +pvr,uroflowmetry,expressed prostatic secretion for culture and sensitivity,urine for AFB.if investigations does not reveal obstruction then u have to do urodynamic study.
hope i have answered ur query. i will available for follow up queries,thank u