Hi, this is my first Yorkie. We got him from a breeder when he was 12 weeks old. He was used to being around his mom/dad, aunt, sister, brother, and cousin. She never even took them outside the potty because she didn't give them their first shots until they were 8 weeks old (afraid of Parvo). So, when we got him, he was very scared of many things. He pottied and pooped a lot in the house. We had read not to scold him but to pick him up quickly telling him no and taking him outside. While he is pottying or pooping, I say, "good potty" or "good poopy" when he looks about done. I then excitedly give him a small treat. He still has accidents but for the most part will do it outside in our back yard (of course we have to stand there with him without engaging him). With Sammy, he will first pee and get a treat. He will then go back out to the yard and search for a spot to poop. He then gets another treat. I also pick up his poop and put it in the garage as I read where they don't like to have their yard poopy.
It is funny that when we first got him, I didn't realize that I have to think of him like I would a baby or a toddler. When toddlers get tired at night, do they say, "I'm ready for bed?" Neither does Sammy--but what he does do is get crazy. I noticed a couple of times when we played with him at night, he would snap at us. I realized he was tired and we put him to bed. It is one way we realize it is time for him to rest. When we first see him, I get on the floor and loosely hold him as he is all over with excitement. After a minute, I take him to potty immediately. Then we can play and take a walk. Mine still doesn't "come" when called. I used to chase him when he had something in his mouth, but a friend told me to rattle some paper to get his attention. They have very short attention spans. He usually drops it and runs for whatever I have.
We have started obedience training. We are also trying to watch the Dog Whisperer (Cesar Millan). I hope this may help you. Sammy doesn't like poop in his area at all, so he will hold it until he gets out in the house

or in the yard (if not more than 9 hours). We are reallllly enjoying ours...I hope you can come to enjoy yours too. I know you will.