Update:
We had our appointment with Simon yesterday morning. BB hadn't been doing great since Sunday night, the tramadol wasn't working either. Upon initially feeling BB, Simon didn't seem concerned. He thought the bladder felt good and couldn't feel BB tensing at all upon it being prodded, he also squeezed a very big pee out of BB which was clear all the way through. We still decided to go ahead and X-ray. We really believed BB was going to be put to sleep, especially if there was a stone as we, and Simon, all know that operating again would be pointless if the stones are constantly reforming.
Anyway, the X-ray showed a stone... however it was only really small. This makes things more complicated but also a lot more positive. BB is still with us. Simon thinks that those moments where the pain relief doesn't work are because the very small stone slightly begins to block the urethra before moving back to the bladder where it should be, which explains why the pain relief works and then it doesn't and then it does again - if that makes sense. He thinks that it's far too small to be causing a great deal of discomfort when it's away from the urethra. Simon urged us to carry on with BB and so we are.
The plan of action is this: we give him loxicom, gabapentin and tramadol and try to manage the pain. If we are unable to manage the pain then BB will be PTS at a local vet. If we can manage the pain, we wait 2-3 months and then go and see Simon again. If there is still only one stone present, we remove it. If another stone has since formed, he is PTS as it means we will be constantly dealing with stone after stone despite removing them. Because of how small it is, Simon believes he can live with it until it becomes bigger in a few months time and waiting means we are able to see if this stone is the last one he will hopefully produce, at least in this quick of a succession, and we can operate for a third time. Simon's only worry between now and when we see him again in 2-3 months is the stone actually entering the urethra which will mean urgently getting BB to the vets for euthanasia - this is a possibility due to how small the stone is.
So for right now, we take each day as it comes. Today he doesn't seem too bad, he had very slight pain this morning when he was due his medication but I haven't heard anything since. We just have to keep going with it and hope it all turns out okay