Hi Kristy, Welcome to JustAnswer. I am a licensed veterinarian and I'll be happy to help. Milo is unfortunately in an emergency condition. When a dog can't breathe well he needs to have oxygen supplementation ASAP while a diagnosis found.
Milo could have a congenital problem with his heart, he could have a diaphragmatic hernia, he could have pneumonia, he could even have migrating round worms. I recommend that you get him emergency care now. I know that it is very late there, but with his difficulty, without any emergency intervention, I'm afraid Milo won't live until morning!
I'm so sorry!