My Angel is recovering from a abdominal disease that we have finally had diagnosed as Lymphangiectasia. We almost lost him several times but after treatment and medications he is almost back to normal. There is no cure but it is managable. His illness started with vomiting and diareah. Then his stomach bloated up and he lost alot of his weight he went from almost 7lbs to 4.9lbs. He was losing protein in his blood. We took him to a specialist and was treated with a transfusion of plasma, and they did a gastrocopy and biopsy of his intestines. I hope and pray that is not what your yorkie has but it should be ruled out with blood test. The website petplace.com can give you more detail about Lyphangiectasia.
http://www.petplace.com/articles/artshow.asp?artID=4769