I am sorry to hear that Brownie is nkt well. From what you are describing and the picture you provided I would be concerned that Brownie has kennel cough. This is a highly contagious respiratory disease passed between dogs. It is particularly common in shelters and kennels. It is caused by a virus, and is usually self limiting in a few weeks. However, it is also possible to get a Bacterial infection in conjunction with the virus. If you also notice creamy discharge this is likely. I would suggest taking Brownie to the veterinarian to have him examined and have an antibiotic prescribed.
When you call to make the appointment please mention the suspicion of kennel cough as they may see you at the end of the day or in another area to prevent the spread of tHe disease.
Here is some mor information on kennel cough and I wish you the best of luck
https://www.petcoach.co/article/top-7-questions-about-kennel-cough-in-dogs-answered/Other possible causes are tracheal collapse and a foreign body obstruction. Though these are less likely. Please feel free to post any further questions you may have here on the forum we are here to help you!