Three possible causes come to mind:
1. Epididymitis
2. Kidney stone
3. Prostatitis

I doubt if there's anything you can do without seeing a physician.  If it's
epididymitis you might not need to see a urologist; my GP was able to treat
it with antibiotics when I had it.

Others may have more wisdom on this subject.

Paul A.

All I can say is that I got mine checked out and it was definitely Chronic
Prostatitis. I went on the strong antibiotics and they had a BIG effect at
first but as most people seem to find out, over time they have less and less
effect and when taking them you are supposed to stay out of direct sunlight
which isn't always possible for me. So, I had to stop taking them. I started
taking about 1500 Grams of Saw Palmetto every day. I was sick in the guts
for about a month when I started and got used to it after that. Pain went
almost away but is still there to an extent. Went off the SP and pain came
back. Went back on and it went again.

Added to that, at the dinner table and in front of this computer, I sit in a
folding camp chair that has calico strung between the wood for you to sit
on. It is a more comfortable way to sit for those of us with this sort of
pain. The SP and that sort of seat help a lot. Get used to getting up and
walking around for no apparent reason to others. It helps ease the pain,
naturally. Oh and don't take pain killers a lot but don't rule out an NSAID
now and then if you aren't allergic to them. Helps me sleep if the pain is a
little too bad.