Sick infant question

So my five week old is sick with a head cold. The doctor we saw today said to watch for a few things, one of which being coughing so hard he vomits. He's done that twice since so I called and another doctor said that since he doesn't have trouble breathing, isn't dehydrated, and doesn't have a fever just to wait and bring him in tomorrow.
Is it wishful thinking that he's throwing up more because he's eating more due to wanting to comfort nurse?
I feel so smurfing helpless.