The mysterious urinary frequency!

Hi there. I am a 21 year old female and for the past year now, I have been having problems with urinary frequency. I feel like I have to pee all the time and I go to the bathroom about once an hour (or more). At night I wake up an average of 2 times to go use the bathroom.

First I thought it was a urinary tract infection. My doctor put me on Antibiotics and nothing happened. I had my urine tested--nothing wrong. I had a bladder and kidney ultrasound--nothing wrong. I had a cystocopy and bladder scope--nothing wrong. I saw a gynecologist who gave me a pap/pelvic exam in case it was related to that but guess what? They didn't find anything wrong.

I have seen two seperate urologists over course of the past year, and I've taken numerous medications for overactive bladder (i.e. Sanctura, Enablex, Detrol LA, Toviaz, Urispaz... and probably more that I'm forgetting) although my symptoms aren't completely in line with overactive bladder. I don't have incontinence and a scan of my bladder showed that I am emptying my bladder fully.

I'm a pretty healthy person in other respects, but I am starting to fear that this problem is never going to go away. I am desperate for any suggestions anyone might have or if anyone has any idea what my problem could be. Thanks!