I'm probably a bit too late with my answer, but I've asked myself the same thing. Are you still struggling with UTI? It's pretty astonishing and rather frustrating that there's so little activity in this part of the forum when you need it, especially since UTI is such a common and painful problem.
Anyway, I hope I can help should you still be struggling. I've had a lot of kidney stones myself and eventually learned that most UTIs are caused by bacteria that stick to the lining of your urinary tract. That's why they keep recurring. For me I'm sure it's a biofilm in one of my kidneys, for you it's probably something similar, although probably not as severe and most likely in the lower part of your urinary tract. Bacteria are not supposed to be there, so you will want to get rid of them once and for all.
The only way to go is by breaking up the biofilm; which is rather difficult, followed by an antibacterial protocol to flush them out of you.
To do this you will need a combination of enzymes to break down the biofilm itself. I use biofilm defense by Kirkman. It's basically a blend of pretty potent digestive enzymes. They are said to work through the biofilm by breaking down the sugars that keep it together. It definitely works, since I now have a pretty severe lower UTI (doesn't make sense I know). But of course, when the biofilm is being broken down, bacteria are being released, which causes the body to begin an inflammatory response, and the now planktonic bacteria to look for a new home elsewhere in your urinary tract. Which is exactly what is causing the relapses and the symptoms or pain to worsen.
All this suggests that it's not enough to simply break down the biofilm, without something to push out the bacteria to prevent a new biofilm in another place. You need to get to the root cause. These bacteria most likely are of the E coli strain. Good news, since these are easily eradicated with a type of Sugar called D-mannose. This Sugar isn't metabolized and therefore very safe to use, even for diabetics. At least that's what I've been told. The E-coli bacteria are fooled by the D-mannose, attach themselves to it after which they are easily flushed out, along with your urine. So, no chance for them to reattach themselves! How great is that? From what I've heard it's very succesful in treating UTIs, more so than antibiotics even. Several people swear it's helped them more than some of the best antibiotics. The D-mannose also doesn't attack healthy bacteria, which is another good reason to try it. However, from what I've read your UTI will need to be caused by a strain of E coli (90% chance at that, so definitely give it a try).
You could still use an antibiotic in a pulsed dosage, which seems to help in eradicating persistent UTIs and biofilms. But, like me, don't take the enzymes alone. You definitely need something to eradicated the bacteria once they leave their matrix. In my opinion, the best thing you can do is to use a combined treatment with all of the above (enzymes + D-mannose + antibiotics in a pulsed dosage). Pulsed dosage means taking the antibiotics in low dosage over a longer period of time. Scientific research suggests this is the most effective way for antibiotics to attack the biofilm formation. Doesn't make much sense, but it seems to make the bacteria more sensitive than a high dose treatment. At least that's what research suggests. It's definitely worth a try. Some doctors will claim that biofilms can't be broken down and that the only solution is either managing it or removing the infected part. Fortunately, there's hope and scientists are now also starting to pick up on the enzyme treatment. Goes to show that alternative medicine isn't always "quackery". In fact it might be one step ahead at times.
I think it's safe to say that when you suffer from relapses, you most likely have some sort of biofilm formation that causes the chronic UTI.
I've heard some pretty good things about D-mannose. I also take a supplement of herbs that grow in Asia, produced by Himalay Herbal Health care and which specifically help the urinary tract. All of this of course, can worsen the symptoms should you do nothing to counter attack the bacteria once they are released from the biofilm matrix. Don't assume your urine and body will take care of them. They easily attach themselves to your cells and to each other. In other words, an increase in pain and burning sensations is normal and a sign that the treatment is working (that is, if you are stupid enough to only take the enzymes like me). Taking the D-mannose together with the enzymes will definitely take care of the planktonics and prevent re-infection and pain. Cranberry is also said to help UTI. But the one thing that seems pretty promising is the D-mannose.
The fact that antibiotics alone didn't cure your UTI, again goes to show that at times, alternative medicine is pretty good competition for your doctor :) Sometimes nature has all the answers. We just need to look for them.
Hope this helps somewhat, if not now, maybe in the future, although I hope you never have to deal with this again. I know how painful it can be.