Without knowing a lot more it's hard to say but on the face of it waiting that long appears too long. If it was me I'd be looking to find the fastest route into finding out why and what can be done about it. You might ask why with a Gleason score of 4+5 it's being treated as non-urgent as an injection only takes 10 minutes, if that's what it is. It might be an oversight and they'll take you in.
Whether to start with the diagnosing doctor and ask why and whether he can refer you to another oncologist perhaps at another hospital, or to go direct to the oncologist. Perhaps to go via Macmillan if there is a nurse to speak to. Although I found the Macmillan nurse didn't seem very helpful when I thought one of my appointments was longer than I expected, but your case may have more foundations. Without knowing more it's hard to say but it seems you have a good case to be given a good reason why or be seen well before then.