I've been having the same problem for about the same time length as you. I noticed when I drink plenty of water I don't have as many infections. I think our bladder gets very sensitive when we have so many infections. It seems anything with acid in it bothers mine. Like orange juice, etc. I have to be careful of everything I drink. I also buy unsweetened cranberry juice from my health food store (in concentrate). I dilute the concentrate with spring water. It seems to help, but it takes several months of drinking the juice before I noticed an improvement. If you try the juice make sure you get it without sugar or it won't help. I haven't beat the infections yet, but I have noticed I don't have them as often. I'm keeping my fingers crossed that eventually the cranberry juice will be the cure. Let me know how you are doing.
My suggestion, with your history, is to go see a UROLOGIST. You didnt say IF your MD has ever done a urine culture or not, but for recurrent UTIs the reason/source is important. Also, you might need testing that shows more info about your bladder and kidneys that lab tests and cranberry therapy cant show.
As for myself I did go to a Urologist, mooksmom. He did a culture and I believe a test called an IVP. Something like that. The test gave him a clear view of my bladder. He told me everything was alright and he had no idea why I continue to get infections. I don't know what else to do. The Urologist didn't have any good suggestions. I am concerned about the constant infections because the doctor told me I could develop polyps in my bladder.
When I went to my Dr he did take a urine sample, but everytime I go back he just tells me the prescription he gave me obviously wasnt strong enough and he either ups my dosage or gives me a new medication, which obviously in the beginning you think that because he's a Dr he obviously knows what hes doing, but after 3 or 4 (plus) times you start questioning that! I think a urologist is a good idea, I have never had any other tests but I believe I should if they are out there and I appreciate your help, I will find one and go there directly myself. The other thing is, the infection is usually triggered after having intercourse with my long term partner, it is actually illegal where I live to have intercourse before marriage (it isnt really inforced but it does make me nervous when answering the question in the Dr's "are you married") do you think this is also worth mentioning, or even taking him with me....?