Aloha! You're speaking to Dr. Michael Salkin
I'm sorry that your question wasn't answered in a timely manner. Hemorrhagic gastroenteritis is actually an umbrella term that refers to hemorrhagic enteritis or colitis
associated with a number of infectious and non-infectious causes and that typically lasts less than a week in duration. We consider intestinal parasites (Giardia, e.g.), viral (parvovirus, coronavirus, e.g.) and bacterial enteropathogens such as Clostridium. There's quite a bit of testing required in patients who don't remiss with conservative therapy. I need to see the results of test results to date to be more informative for you and I'd like to know which drugs have been administered so far as well.
Can you upload a copy of his test results to our conversation? I understand that you might not have a copy of the results at home but his vet should be able to give you one which you could scan into your computer and give me the link or you can photograph the page(s) and upload the images by using the paperclip icon in the toolbar above your message box (not if you're using the chrome browser) or by using an external app such as imgur.com or dropbox.com.
I don't have a ready answer for his "funny random gag cough" at this time. He may have picked up kennel cough
at the vet hospital or, conversely, more serious cardiovascular or lower respiratory disease is present. How old is your dog, which breed is he, and does he have any pre-existing medical history that might pertain to his current illness?