Sounds like what my Abbi had when she was about 5 months old. It was coccidia. See here:
http://www.yorkietalk.com/forums/yor...ccidiosis.html
The runny stools were really horrible smelling and she was very dehydrated. I fed her pumpkin, boiled chicken, brown rice, plain yogurt and gave her pedialyte via syringe to make sure she was hydrated and had some electrolytes.
Good luck!!
Michele :-)