I was HDR brachy, so not quite the same, but the symptoms match, if not the timing. (Mine was in the month after treatment, but my treatment lasted for 20 mins, yours is nearer 6 months.) I also had external beam radiotherapy, but I think most of the side effects (except bowels) came from the HDR brachy.
Depending on the isotope, you are coming to the end of the LDR radiotherapy around now, and the side effects are delayed by some weeks, so I would expect to be diminishing any time now. I did have an infection at tip of penis after the procedure caused by the catheter (which was only in for 24h). Although the infection had gone in a week, it took some months to heal so it wasn't painful anymore, and the pee stream returned to normal shape.
Another possibility - your brain has a body map to map pain on to, so you know where pain is coming from. Some parts of male urology (such as the prostate) are not on this map, and your brain may map such pain onto the penis, particularly the tip, so this can be referred pain and not the actual location.
For bowel movements, I had to switch to a low fibre diet. I still can't eat the amount of fibre I did before, but I can now eat most fruit and veg. For peeing, you might like to lookup bladder retraining.