The ivermectin just makes me nervous. A Preventic collar can be a low dose alternative to help with mites (same family as ticks). We had a very itchy dog on the GSD forum - after everything, it was antibiotic treatment that worked, as it appeared to be a low level staff infection. I dunno, itxhy dogs are so tough.
Ham, usually a very bad food - highly processed, high salt, etc. Better if you can buy some lean pork (if pork is tolerated), bake it up, cut, and feed. If you are a memebr of Costco, definitely the best price - you want to get the chops, unprocessed. Fed my allergy girl this for nearly a decade.
I also used steamed green beans with her (frozen pack from Costco is most economical). The boy here seems to be allergic to them, they are in the legume family, and he's allergic to peanuts, so they must share a similar protein. Peas might give more substance, but being very starchy, might not be tolerated. Squashes, sometimes pumkin can be tolerated. For my limited boy, I feed some olives, beets (non-pickled), water chestnut, sauerkraut, a touch of artichoke hearts, and a small bit of a brocoolli and cauliflower mix. Carrots are an allergen here. I use coconut oil, and a touch of organic safflower oil when he gets o-6 deficient.
Eggs are a great form of protein and good fat if tolerated. I'm assuming that eggs and diary are not on the allergy list then?
Probiotics are important. If fish is tolerated, I would try fish oil, maybe borage oil, if it appears that oils are lacking - sometimes just these things alone can help with the itchies. I always covered my bases with a multivitamin, and a B complex.