The first thing that you have to get out of your mind is the guilt of having a STD some time in your life, resulting in urinary frequency all your life. An infection of the urethra or urine may cause urinary frequency, but it would persist only for the duration of the infection. A persisting urinary frequency is more likely a result of decreased bladder capacity or increased urine formation. Increased urine volume may occur as a result of a habit of taking excessive fluids, diabetes mellitus, diabetes insipidus (the brain pituitary defect you are talking about) or a result of taking some diuretics advised by your physician. Permanent decrease in bladder capacity may also result in frequency as a result of contracted bladder due to some diseases. First and foremost thing is to know whether it is the increase in output that is bothering you, or a decrease in bladder capacity. A simple test is a voiding diary for the whole day, where you will list the time and your voided volume of urine continuously for 24 hours. Let your doctor see you with this diary, and I am sure he would be able to suggest you something constructive to take care of your problem.