My heart aches for your sweet pup. The famous holistic vetdr. marty goldstein, https://drmarty.com/ now retired has great book on natural healing that provides some suggestions. I tried slippery elm and it worked, more information here, https://www.whole-dog-journal.com/care/slippery-elm-for-dogs-safely-treat-irritation/
In the gastrointestinal tract, slippery elm acts directly. Think of it as a natural Pepto-Bismol (Pepto-Bismol itself should be used with caution because it contains salicylate, a.k.a. aspirin). Slippery elm’s mucilage content coats, soothes, and lubricates the mucus membranes lining the digestive tract. Slippery elm is an excellent treatment for ulcers, gastritis, colitis, and other inflammatory bowel problems. It is high in fiber, and so helps normalize intestinal action; it can be used to relieve both diarrhea and constipation. It may also help alleviate nausea and vomiting in dogs suffering from non-GI illnesses, such as kidney disease. A syrup made from slippery elm bark (see recipe below) can be used to help heal mouth ulcers.
Slippery elm is said to relieve inflammation of virtually any mucus membrane, and has been used in the treatment of inflammatory conditions of the lungs (bronchitis, asthma), kidneys, bladder (cystitis), throat (tonsillitis), and joints (arthritis).
This wonder herb also contains many nutrients (carbohydrates, protein, fat, ascorbic acid, beta-carotene, calcium, and several trace minerals) that can be beneficial for dogs recuperating from any illness, and it may stay down when other foods are not tolerated.
Externally, a soothing paste of slippery elm powder (mix the powder with a little cold water) can be used as a poultice for hot spots, insect burns, rashes, scratches, ulcerated areas, or other shallow wounds. Native Americans used slippery elm bark to stop bleeding. It forms a natural bandage that can be left in place for several hours, if you can convince your dog to leave it alone! Moisten with water to remove it.
I used it with applesauce (unsweetened). Good Luck and keep us posted on his progress.
on basenji # 5