What causes bladder pain in men? have no stones or infection?

A condition called intersticial cystitis is one cause. But the main need may be is to determine if pain really originates in the bladder. Vague low pelvic pain, often including the rectal area, the testicles and the penis often is due to the chronic pelvic pain syndrome, once considered a form of non-infectious prostatitis. Google it for more information and see a urologist. Good luck.

There are many causes other than those- interstitial cystitis, prostate, bowel adhering to bladder, retention of urine, etc.