You should never attach your leash to a collar on a Yorkie. They tend to have a very delicate trachea that can be damaged easily by the pulling of a collar on their necks. Some people use a ferret harness on their puppy until they are big enough for a regular harness.
You might want to try getting an exercise pen to leave him in while you are gone. If you put a pee pad in there with him he might actually use it instead of the floor. If you want to outside train him then you are going to have to keep your eyes on him every second and take him outside often and whenever it looks like he is about to pee or poo. Try taking him to the same place each time and saying something like "go pee" or whatever terms you use. That way he will learn why he is out there. As soon as he does his business praise him greatly and take him directly inside. Don't mix outside play time with potty time or it will be more difficult for him to learn what he is supposed to be doing.The muscle that is needed for a puppy to hold their urine does not develop until they are around 16 weeks old so at this point it is all about
your timing and getting his little brain to associate peeing with being outside. Little dogs have little bladders so they often have to go out more than a bigger dog would. If you do a good job of training him he will learn to let you know when he needs to go out. I think many times dogs do not get properly trained because people do not watch them closely enough and they give them too much freedom in the home before they are ready.
Dogs just love stinky thing and items that have our scent on them. Even cute little darlings like Yorkies have this trait!
I guess I would call the people you got your pup from "backyard breeders." They may mean no harm but they are not doing well by those dogs. No competent breeder would let a puppy leave it's mom before it is totally weaned and ready physically and emotionally to be on it's own. The thought of fleas crawling on helpless babies is just terrible. I'm sure you have a darling little puppy and I hope things go well for you with him. There is a lot of information here about Yorkies and I hope you get time to read some of it. Welcome to YT and congratulations on your new puppy.