Hi and Welcome to YT! I am so sorry that your baby is sick. It's very important that he drink, especially if he is vomiting. The link that Yorkiesmiles posted for my "Nonnie's Magic Broth" is wonderful to use when they won't eat or drink!
http://www.yorkietalk.com/forums/1978087-post75.html They also love the chicken as it is so tender you can almost mash it up with your fingers. If you don't have time to make this ... I have used the Swanson's Low Sodium Chicken Broth [canned] and my Toto will drink that but not like she laps up the fresh broth.
I will keep your baby in my prayers. Please update us and if there is anything more that you need, just post here.