My little Emma did the same thing, I bought some deter medicine (it had pepper, yeast, and some other ingredients in it) and gave her a 1/4 of the tablet everyday for a week. She was also tiny, only 1.5 lbs and she did fine. It only took one week and I haven't seen her touch a turd yet! lol I don't know about the nutrtion aspect with her poo playing. I would recommend you switch to a better brand though just in general. I love Innova and Solid Gold. Here is some information about the different foods and how there are many that are much healthier for your pup
http://www.yorkietalk.com/forums/yor...ing-chart.html
Good luck!