I don't think the oleander soup should be a problem, afer all even at the maximum dose you are only using a tablespoon or so of the "soup" in the enema. Why not use a rectal syringe instead of an enema? Either way, you can add in the colloidal silver when you take it rectally.
Insofar as the itch, have you introduced any new household chemicals during the same time you developed the itch? Air freshener, new detergent, cleaning product, etc. The air cleaner/freshener Oust once gave me a bad reaction (though I did develop bumps all over). In my case, I tried just about everything and ONLY benedryl worked (plus I cleaned all the household surface, including my work area, with diluted vinegar).