An enlarged prostate makes urinating more difficult by narrowing the urethra, but generally this does effect men over 50 years of age.
I don't know your full medical history etc., but there could be a blockage which is causing the urine stream to split, it could indicate and STD, could be inflammation in the urethra, start of a yeast infection. You state you had a urine sample and it was clear of bacteria, if this was only done in the office, I would also suggest to have a urine culture done, where a urine sample is sent into the lab along with a swabbing of the penis as well, to rule out any bacterial infection, STD etc.
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