I found something very effective for long lasting constant urethral pain (it started post infection).  All tests I underwent were negative.  I got antibiotics anyway but it did not help at all. The pain was there all the time, not only after urinating.

I bought NUROFEN RAPID (it is liquid ibuprofen in capsules and it is an anti-inflammatory). I pierced a capsule and applied some of the liquid directly on my urethra.  I got strong burning pain that lasted for about five minutes and it was really horrible but after that, everything, including my urethra slowly stopped hurting. The day after, all pain from my urethra was gone. The pain came back some days later and I used it again. This happened several times.  Now I have been without pain completely for about three weeks.

When I took ibuprofen orally, it had no effect, only the topically applied one. Apply it before going to bed so that it stays there whole night.

(I have posted here before that I also had some relief when I used Betadine ointment).