It seems strange to me that he is passing so much waste if he is impacted, This sounds more like an air bubble to me, hopefully some larger food i.e earthworm will help....of course Bellaballo Is A LOT more knowledgeable than me just throwing that out there.
I am sorry If you think I am calling you an idiot, I mean no offence just being thorough, do you de-frost the bloodworm cube before throwing in your tank?
Keep trying with the earthworm, my leucistic was such a hard sell when it came to earthworms but eventually he realised he loves worms, Try soaking the worm for a while before feeding if you are using 'dandrobaena' (sp?) they excrete a yellow 'liquid' that repels potential predators.
Also I was under the impression it is potentially dangerous to fridge such a small axolotl, am I wrong? I would like to know for future reference.
I really hope you solve this problem, it sounds like you are doing everything in your power to make him comfortable.
Good luck