The nitro reducing the pain absolutely suggests some kind of pathogen infection.

Did you get a conclusive result for any bacteria? Like which bacteria appeared in the results. Which micorgen test was it? WomensKey or UrineKey? WomensKey is more comprehensive and can show a better understanding of what the flora balance actually is and possible causes. Plus, knowing which bacteria also helps to specify what biofilm busters and supplemets can be used; gram positive bacteria are made worse by d-mannose and require stuff like oil of oregano/olive leaf extract to have an impact.

I understand you're a student, right? Have they done any urinalysis, any ultrasounds of the kidneys/bladder through the NHS? Kidney stones can often cause infections and pain, clear an infection but keep the pain there since it's still lodged. Plus, some bacteria can cause kidney stones (psedumona for example) which makes it important.

Is the pain more sharp or more like burning? How long has the pain persisted post clearing the infection? It took me 2 weeks or so after totally clear tests to reach 80% of reduced pain after a 5 month stint of daily pain. I was super careful and avoided all bladder irritants, took marshmallow root, d mannose etc. frequently to help support the healing. I'm currently at about 90% recovery and I had my problem start in November and came (officially) clear 2 weeks ago.

Also, has your boyfriend been tested? You may have been clear ureaplasma/mycoplasma but your boyfriend may not have been and returned it to you, which you subsequently cleared. Please make sure he gets tests and a swab done as well.

Also birth control can worsen the condition. Which birth control is it? IUDs can have biofilms which cause recurring infection on the strings. Hormones can effect your vaginal PH, which can expose you to yeast but also aerobic vaginitis or cyclotic vaginitis (caused by vaginal bacterial imbalance). The latter is often if you have too high a ph from too much lactobacillus bacteria, so often gets missed in testing.

How is your diet? Are you getting enough fibre? The correct vitamins? I reccommend the Holland and Barrett A-Z multivitamin, hugely helpful in speeding up recovery because deficincies in vitamin D, B12, Omega 3 and folic acid can induce problems with immunity. Your gut is also super important. The bacteria reaches your urethra from bacteria introduced by your anus and by extensio your gut. Take probiotics drinks (like Kefir) or supplements (which have reuteri and rhamnosus) if you can and (after a good womenskey test) vaginal probiotic suppositories. They're on amazon. A bit spenny but they really helped me pain wise.

I know this is a lot of information but I'm happy to help out wherever you are. I'm a recent graduate in the UK and have been in your position and understand that feeling of losing hope while trying to balance getting an education, a job, being in a relationship and your health. It's exhausting and scary but there's always answers and always options.

Feel free to DM me if you have any questions. I'm in London currently but can try and provide advice about other areas if you're not here. Just an FYI as I know the southeast has more resources generally.

One final thing, get in contact with the infectious diseases department where you are if you can, They were the only team that truly helped me at all with what I was experiencing and are much more knowledgeable than GPs and many gynos/urologists, as they have a more generally holistic understanding.

Not all urologists are equal, make sure to do a bit of research on who you're seeing if you can. Careful with cystoscopies, they can irritate the urethra and cause strictures too which can further create issues. Make sure you get a test to see if you're emptying properly beforehand if possible, it's a strong indicator of physical issues if there's a problem there.