I'm a healthy 42 yo male.  No health issues (no diabetes, no hypertension;
non-smoker; etc).

I have however previously had UTIs (2 or 3 times) in the past 15--20 years.
Symptoms were always fairly subtle (mainly feeling of never emptying
bladder) and after Dx with MD always went away quickly with antibiotic
treatment.  No obvious reason for the UTIs (no anal sex, etc), though they
did always occur when I was in a sexual relationship.  (I always assumed it
was bacterial flora from sex, plus some sort of pathology in my urinary
tract that caused it, though never saw a urologist.)

Last week, I noticed an increase in freq of urination.  Then I started
getting the "bladder never feels empty" symptom.  I assumed it was a UTI,
and as I was out of town on a trip, got some Bactrim from a relative whose a
health practitioner.

The next two days the symptoms got worse:  increasing difficulty urinating,
and felt bad (weak, tired), though had no fever.  After about 48 hours of
that went to ER; quick urinalysis there said that there was no white or red
blood cells or bacteria in urine, so they suggested that if I had a UTI it
was cured by the Bactrim.

Since then (about four days ago), the symptoms have improved:  no more
general weakness, improving urination.  Right now the main symptom is
"bladder never feels empty."

My sister (an internist) suggested over the phone that I might have
prostatitis.  This seems reasonable, insofar as every time I had a UTI
before, (a) I didn't have the "feel terrible" symptom, and (b) things
resolved very quickly with antibiotics.

Got back into town tonight and am seeing my internist tomorrow.

Is this time course suggestive of acute bacterial prostatitis?

More generally, since UTIs are rare in men, what sort of urinary pathology
would lead me to get them?

TIA