I have chronic utis that never go away, what is a permanent sol?

Ever since I was a little girl, I have had a problem with chronic urinary tract infections. Even when I was six years old I would get them and it would be extremely painful to urinate. I would seek comfort in sitting in a warm bath of water (which I know may make the problem worse, but gave me temporary relief). It seems to have only gotten worse the older I get. I am 20 years old and became sexually active when I was 17. It was at that age that I began to get 3 or more utis a month. My gynocologist just always gave me antibiotics whenever a uti got really bad. I have also taken cranberry pills, drink lots of water, and pee after sex to try and avoid these painful infections. Finally after two years of getting utis my Gynocologist said I needed to go to a urologist. They did an ultrasound of my bladder and took a CAT scan and found nothing wrong with me anatomically. However, I remember my Gyno once saying that my urethra and vagina were quite close and this might be why I suffer from these infections. She also said that as I got older they would dissipate as I began to have less sex. At that time I was having sex two or more times a week, but I now only have sex once a week, sometimes even less, and still suffer the same painful infections. All my urologist did was prescribe me the same antibiotic which I have been using for the past 3 years. It seems like I always have a uti or feel that I am on the verge of getting one. I truly feel like these will never go away.

Please help.