So you're right that this is not normal, and I'm glad that you are seeking medical care for this. The key question is where the bleeding is from. From your description is sounds like you're bleeding bright red blood from your penis rather than seeing blood in your urine, which makes a urinary source of bleeding less likely (that would include your bladder, ureters, and kidneys). Given that the bleeding seems to be associated with sexual activity you are most likely having bleeding from the urethra or the prostate, which can be caused by friction or irritation to the organs. Your doctors
are right that infections can also cause bleeding, and this can include sexually transmitted infections or infections of the prostate. Cancer of the prostate could also cause bleeding, but given your age this is much less likely. It's a little unclear from your question whether you've had a cystoscopy done, but the cystoscopy, STI testing and prostate exam are all good things to test. I would recommend that you go back to the urologist
and explain that you're still having bleeding. They may feel that the bleeding does not represent anything serious, but it would be good to discuss your symptoms again with them to make sure that there's nothing else that they would want to do to work up this problem.