What Causes Burning Sensation In The Urethra Inspite Of Taking Treatment?

my mother is sufering from burning sensation in her urethra part for past 1 year ...she had gone for several check-ups,, one of d Dr had advised her to go through d test called crestocopy..and confirmed that there is no serious prob,,, just might be a normal infection which has caused that. but from then she was given some monthly course tablets, but STILL SHE HAS D SAME COMPLAINT VERY FREQUENTLY. PLEASE DO ADVICE.