It's a bummer.

I have a somewhat similar problem, but not quite as bad.

Supposedly, the problem is due to inflammation around the urethra
causing the surrounding tissue to close in and make it hard to urinate.
When you finally force some out because it won't hold any longer,
only enough comes out to just relieve the immediate pressure.  Your
bladder is still pretty full and it's not long at all before you need to do
it again.

You might ask your doctor about:

1. Flowmax, if you aren't already on it.
2. Ibuprofen or other over the counter anti-inflammatory
3. Ice - though the urethra is buried far enough below the
   surface that it won't do a lot of good to relieve inflammation.

If it gets really, really bad so that you feel that you can't urinate at
all in spite of a lot of pressure, there are steroidal anti-inflammatories
that may help a lot.  But of course those things aren't good for you
and aren't for prolonged use.  My doctor gave me one injection of
something like that at the very beginning when I was about to bust
my bladder, and it did the trick for about 12 hours or so.

Let us know how you make out with it over time.  Hopefully the
inflammation will abate, but it might take a few weeks.  I'm going on
two weeks post HDR brachytherapy.  I'm probably at about 10-12
bathroom visits per day, down from a high of 8 in one night.  I still
have a way to go.