Hi... I feel compelled to comment on this thread, because this was me, 3 months ago. My boy was sheer terror, especially because he was teething and very sharp puppy teeth. My arms and legs were badly bitten and more than one occasion, I almost gave up on him but I'm so glad I didn't.
Unfortunately, what you are experiencing is rather common. I have a silky terrier, which isn't much bigger than a yorkie, and I know how much damage their little body can do. I would guess that the problem is that he doesn't see you as his pack leader and since there isn't any house rules to follow, he acts out and tests the water. Try practicing 'nothing in life is free' motto, meaning he has to work for things, i.e. sit nicely before you give him treats. If he grabs something he's not supposed to, try to trade it with higher value item. Find out if he's food or toy motivated and use that - mine would drop anything at the mention of "cheese". If he's acting particularly badly, take him to another room (dogproof-ed of course) that has nothing that would interest him and leave him there for a few minutes. Don't budge when he whines or cries out, but when he's quiet, take him out. Rinse, lather, repeat until he associates praises and treats and playtime with nice behaviour and vice versa.
Definitely get a behaviourist who would help you restore the pack order with positive methods. I was advised by a trainer to get my dog on medication as well but after consulting with other dog owners, I learnt that medication should be used as last resort for adult dog, and to exhaust every other resources before even thinking of prescribing it to a puppy. All the best
