
I have been through all this with my JRT and finally got referred to a specialist who done an endoscopy and found all his stomach inflamed and lumpy and his intestines inflamed. Biopsies were taken and it points to either allergy or IBS. Diet change hasn't helped. He is taking Zantac but reacts to steroids and breaks out in ulcers so is now going onto Atopica to see if he can tolerate it, if it will help him.
If your dog is lethargic at times keep a check several times a day on the colour of his gums, as Milo gets anemic quite a bit due to bleeding in his stomach.
Good Luck its very worrying isn't it and heartbreaking to see them not well for so long.
Just edited to add although Arden grange is a good food on paper a dog food is only good if it suits the dog.
My JRT cannot tolerate any dried food and the nearest we have got him to tolerating something is Nature diet.