I've been having the same issue for about six months now. I saw a urologist two months ago about this because, as it is for you, it was driving me nuts
During the first visit the doctor ordered blood work and gave me the wonderful (read--awful with a big twist of sarcasm) DRE and ordered a blood test. Upon examination, he said that my prostate was roughly the size of a twenty year old man's--15 ounces, if memory serves. (I'm thirty-eight but don't feel a day over, oh, about sixty-five.) He also gave me samples of a medicine called Uroxatral, which is an alpha blocker for the symptoms of BPH.
And off I went.
I saw him again in three weeks to a month later. He said that the blood test, which measured PSA (and maybe a free PSA, I think), showed no abnormalities. Lucky for me he performed another DRE, and then I had the following done to me:
1) bladder sonogram
2) peak flow meter test (the one where you pee into a plastic cup-looking thing)
The bladder sonogram showed nothing abnormal. The peak flow meter showed a small degree of obstruction. He said that the overall results indicated two possiblities:
1) That my prostate was growing around the urethra and compressing it slightly. In this case, the uroxotral should work well. (I had some improvement with the samples of this medication, and although he wrote me a prescription for ninety additional pills and I got it filled, I only took another two weeks worth because I had a very rare side affect from taking the medicine--chest tightness; lovely.)
2) That I had some scar tissue from an old injury and that the buildup of the tissue was not allowing the urine to free flow through the urethra as it should. He said the solution for this is a cystoscopy, where he would insert a small tube with a scope into my penis, find the obstructing tissue, lance it (or whatever the technical term is), and then I would be good to go. He equated the feeling of having the scope inserted as having a strong urge to pee--nothing more. Well, I had the procedure about ten years ago, and for me, it hurt like bloody hell (something about my smooth muscle being a bit thick in certain places; whatever the reason, I won't have another such procedures unless I absolutely must.)
My completely unsubstantiated guess is that I have a combination a one and two. Two, because when I was eighteen, I made the mistake of playing street hockey without a cup and took a slapshot full on from a very good hockey player from only a few feet away. It was very cold that day, and the puck pretty freaking hard. I stopped that damned shot, though
The same guy who took the slapshot also took a few shots (punches) at my groin when we were kids (please don't ask; it was just a phase he went through or something; I have no clue).
I hope this helped a little. I know how frustrating this problem is. I'm going to just try to grin and bear it for as long as I can (maybe until a few drips becomes a few too many drips, whatever that number might be) and then have the damned cystoscopy. I hope I did not scare you off from having the cystoscopy. Please see a urologist and let me know how it turns out for you. Maybe we can share our experiences on this site and help other guys going through the same thing.