if you enjoying reading....the two books i would add to my list
1) four paws five direction by vet cheryl schwart
2) homeopathic care for dogs and cats by vet don hamilton ****** get this one first it is very easy to read very easy to follow anyone doing hoeopathic care has this book....

both books go to cod liver oil one capsule a day. .....vit c start at 500mg and go to 1000mg after two weeks...drop back down if upset stomach.... (you can get vit c from your local drug store) or grocery store....

i also use this and that is honey...natural combs...this is the best immunity booster....charlie had to have several eye surgeries and i gave him natural honey two days prior and two days after...my vet could not beieve how fast he healed....
so i would go with 1/2 teaspoon a day till you see improvement....
******this is natural honey NO additives no squeeze bottle stuff.....you should be able to get it from a health food store....
i use 1/2 teaspoon every three days to keep up a healthy immunity system....as i do not use vaccines....and my dogs come to my grooming shop every day....