Welcome to Yorkie talk...
I am a newbie too. I have three Yorkies and my smallest is 5 months old and weighed in at a Whopping 2.8 lbs today. I use Trifexis for all three of them. It is a pill you give them once a month. It covers Fleas, heartworm and round worm and large worms. I love it! Just give it to them in a small piece of meat or cheese right after they have their breakfast. Since Naevia is so small she only gets a half of a pill.