Frequent Urination Question

Okay here is my story. So a couple weeks ago I noticed I had to urinate constantly, I felt the urge every 10 15 minutes or so and about a week afterwards (after drinking tons of water and a whole container of cranberry juice) I saw a doctor. Obviously, I assumed that I had a urinary tract infection. I had the symptoms, with the exception of the burning penis or burning sensation when I urinate. But when the doctor tested my urine the results said it was 100% clean healthy urine. The doctor told me that maybe calcium grains were somehow irritating my urethra and that If I passed any to then that is typically the problem, and I haven't noticed anything like that. After that I took Azo for two days and that sort of helped I guess (because it numbs the bladder). But now it has been two weeks and the condition has improved quite a bit. Now instead of every 15 minutes or so its like I get the urge to pee every 30 minutes but it is a small urge and I usually just hold it in for about an hour and a half - two hours until i really have to piss. I've been taking Saw Palmetto pills as well, and that doesn't seem to be greatly doing anything. Frankly Im sick of it and I am wondering what it could be. I think I might know the cause to be drinking way to much caffenine but I'm just not sure what option to take to cure this annoying urge. Do I have to submit to drugs or is there some type of dietary way of curing this? I just have no idea and it has been too long. I would really appreciate your advice.

Thanks,
Dan