I had a spell of Prostatitis 20+ years ago. I remember passing blood, which drew some alarm from the urologist. As you say it is a black art or syndrome, in other words no one knows much about it or the treatment. I was under a huge amount of stress at the time, a common trigger for endless bad conditions.
I remember my local doctor putting me on the max dosage of an antibiotic for something like 6 months, yes really, which later drew some furrowed brows (though of course no words) from the urologist. The doctor had said that it was hard to penetrate the prostate, hence the massive dose of antibiotics needed, but there must be a shed load of collateral damage to your body from all that. I had an endoscopy into the bladder, in those days under general (not nowadays) with everything 'normal' they said. It's no fun feeling things aren't right down there. You might find prostate massage helps if you can find someone willing to help, or that regular ejaculation helps. I do believe arousal without ejaculation is hard on the prostate, I read a urologist's comment to that effect too. You mention BPH and there are drugs aimed at that, but I'll briefly mention Tadalfil (generic Cialis) which is taken to boost erectile performance but can also help with BPH. Anything is worth a shot when you're getting desperate.
This website is very good for info though sadly is now slowly closing its doors:
https://prostatitis.org/
It states on the front page:
By far, the most common type of prostatitis is nonbacterial prostatitis. Symptoms may include frequent urination and pain in the lower abdomen or lower back area. Causes may be stress and irregular sexual activity.
And nonbacterial means antibiotics are useless. Mine went away eventually, as the stress I suspected was as a major trigger. Good luck.