Linda and Bob,
I had the same problem. At 6 weeks post-surgery, the back pressure had become quite painful, the penis swelled with the pressure when I urinated, the stream was very small and it went in all sorts of directions. The term the doctor used (and that I looked up on the iternet) was a urethral stricture. It can be caused by scar tissure or irritation and mine was very near the end of the urethra (I could tell by the feeling of backpressure eminating from that point.
The surgeon actually cleared it in a sugery center (15 minutes under anesthesia) and it helped immensely. However, seven weeks later, it came back.
This time, he was concerned that the stricture was further up the urethra (it wasn't) and used a probe to check (yup, that hurt). This time, he also used 4 increasingly-large probes to tear it up (hurt even more when he did it, but the pain was gone immediately when he was done). There was a bit of blood, but immediate relief. Also, this time he provide a plastic urethral dilator that I am to use twice a day for a few weeks to keep it open until it is entirely healed. Luckily the dilator doesn't hurt at all.
Anyway, from your description, it some like Bob may have something very similar. Easy to fix and only momentary pain.
Biopsy June 21, 2006
PSA 6.1, Gleason 3+3=6 in 4 of 12 cores
Radical Robotic Prostatectomy September 13, 2006
1st post-surgery PSA on October 19 = 0