Yes I had this problem too and was offered flomax (tamsulosin) towards the end of RT.
I decided against it, it wasn't something that bothered me that much.

At 6 weeks post treatment followup, it was not improving and I was offered it again with an anti inflammatory (Celebrex = Celecoxib) for 10 days.

I said I would take it if it would help curatively. The doctor said that reducing the inflammation would allow it to heal (I was a bit sceptical).

The pain did disappear after about a week of medication but came back a week after stopping the celebrex, pain was less though. Since then slowly the pain has dimisished, it's almost not there now. It probably just took time to heal but I was a bit worried it might be chronic.
I will stop the tamulosin soon as well.

Good advice from @northoftheborder about food/drinks (although weirdly wine improved my symptoms!)

Talk to your doctor/nurse/technician after treatment. At my hospital it was nurses who did it and there was always a (junior) doctor on hand for this sort of thing.