Bad Dog Rash on my Akita Puppy...... please help

my Akita  mix with rotweiler puppy is 6 months and recently got the most disgusting pusey bleeding rash that spread all over his body. My other dogs are fine and we have tryed everything. The vet wants to put him to sleep because the skin is so bad he is miserable. I live in a small caribbean island and im not sure how good the vets are here i was wondering if anyone could help me figure out what is wrong with my pup.

We have changed his diet a few times and tryed antibiotics and cremes but nothing is working..... PLEASE HELP!

[Aleda M Cheng, D.V.M., C.V.A]

I really want to help you and your puppy.  Could you please list everything that your vet has tried so far such as: has your vet performed a skin scraping and checked for scabies or demodex mites?  Do you use a flea and tick preventative?  Do you use medicated shampoos?  What antibiotics have been tried?  Has prednisone helped? etc, etc.

Thanks.