A 1/2 cup of food at one meal is a lot of food for a Yorkie. My 3 are all over 10+ pounds and they only eat twice a day 1/3 cup of food. As for the itching, there is a real possibility that it is from either one of the food that you are feeding. I would make an appointment for the vet regarding the throwing up. Switching foods might not be a bad idea. Benadryl might help for the scratching and itchiness but I would talk to the vet before starting this to rule out other issues.
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