My urine stream is bifurcated, and behaves abnormally, but I allegedly have no obstructions (a ureteral stricture was thought to be causing this), my pressure's fine, and there are no physical abnormalities. Why does it behave like this? 
Before I begin, let me give background incase it may help anyone who reads this that cares, I'm an 18 year old non-sexually active white male with an average sized, circumcised penis who is 5'10 and right around 185 pounds with no family history of the issue. Anyway, let me hop in: it started roughly 5 years ago when I went to urinate the stream would do odd things such as bifurcating with one stream going the right way and a lesser stream going off to an angle or that lesser stream sometimes turning into dribbles that would occasionally drip back onto my pants, and it seems to have gotten marginally worse since then as my penis has grown. Suffice to say, I have peed sitting down for well into 2 years now, which as I'm sure you can guess, I would prefer not to have to do in public places. Moving on, about 9 months ago, while on vacation in Arizona I became very sick and eventually went to the hospital with magenta colored urine where I found out I had a UTI. When I told the doctor that I was not sexually active he didn't know how I contracted the illness, but when I told him of my difficulties with urination he suggested it was possible that I had a ureteral stricture and it could have blocked something that became infected. While I was in the hospital a Urologist did come by my hospital room to give me his diagnosis; after inspecting my penis and not seeing any noticeable physical abnormalities he came to the same conclusion as the hospitalist who had suggested that it was a stricture. (character limit).

I then went home several days later after I was well and immediately got an appointment with my primary for a referral to a Urologist (my insurance requires it). It took them a few months because of several issues, but eventually the referral did go out and I was able to visit a Urologist who suggested after inspecting my penis and as well finding no abnormalities that I should come back in a few weeks to get scoped to look for obstructions. A month or so later after the scoping I went back in for another visit and he told me that he did not see any obstructions and that he wanted to schedule me for a pressure test as that may be why the stream was not right. So I went back in for the pressure test (not fun!), and after I was called back in a week or two later he told me everything looked normal, though I was not able to fully empty my bladder, and proscribed flomax and told me I should take this and see if it works as he would not suggest surgery for someone so young. I didn't take it for awhile because I lost the pill bottle, but I found it yesterday and started taking it again, only to find no change in my urination, but a change in my ejaculation yesterday (almost nothing escaped the penis). I hoped maybe it was a fluke, but again the same thing happened today (this possible side effect was never even explained to me), and there was still absolutely no change to the urination.