Why Is My Dog Coughing Up White Foam And Clear Liquid?

My husband and I adopted a dog from the local animal shelter last week. I took him to the vet just for a check up the day after we brought him home. He had hook worms and whip worms. I’ve given him the 3 day treatment for the worms already. He’s eating and drinking normally and doesn’t seem overly tired or lethargic, but late last night he started vomiting/coughing/gagging. He starts with a deep almost chesty cough and gags then throws up a white foam/clear liquid. Every once in a while he also coughs up a thicker mucus almost and his nose runs quite a bit. He’s also breathing a little heavily, but he’s done that for as long as we’ve had him. Any advice would be greatly appreciated. We’re going to the vet first thing in the morning, but any advice on how I can treat his symptoms temporarily or help make him more comfortable would be great. Any insight as to what this might be would be appreciated as well so we’re not totally unprepared at the dr’s tomorrow. Thanks so much!