First off I am sorry for the loss of Slayer
what were your temps hot and cold side?
what was the humidity level at?
pinky mice or rats?
was your vet a reptile vet or just a normal vet?
was the antibiotic cream pain relief?
was your heat source regulated?
in order to find the cause we are going to need every piece of information you can think of and then some tho red spots under the scales and bubbles out the mouth and nose makes me think of a respiratory infection