Hair Loss/Allergies

Question
My question is actually about my Portuguese Water Dog, but since Poodles are there biological cousins, this should be a fit. One of my PWDs came down with a terrible case of scratching and itching recently, that I can only attribute to seasonal allergies. He is coming up on his 2nd birthday and this has been a bad season and my other 3 PWDs also itch, but not this bad.

I took him to my Vet because he developed bad cuts and sores from scratching. We ultimately had to put him on antibiotics and Prednisone to stop the scratching, which is working. However, last night, while petting his back, I noticed a sticky spot and brushed it and exposed a small nickel sized spot of flesh. The hair and skin was in a gooey pile.

My Vet says this is not a reaction to the drugs and I am at a loss for what he could be allergic to, having removed and re-introduced almost every thing he comes in contact with at home. He was recently rolling in some juniper bushes on my property so I had them removed, but I found out that juniper is medicinal and he may have been trying to seek some relief himself.

I am in NJ, do you have any idea what could be causing the allergies and hair loss?  Thanks.

Answer
Follow up:
First off red mange is genetic and DOES NOT just occur in puppies.  Puppies and older dogs tend to be the ones that you see it come out in most offen as they usually have more compromised immune systems but a dog of ANY AGE can get red mange.  So I am NOT off base on that one.  I have done a LOT of research on mange and I DO know what I am talking about.  Second off you never said that food have been ruled out.  No where in your question do you address the issue of food.  You asked me for my oppinion and then are mad at me because I suggested genetic causes?  Why ask me a question if you are going to get upset and my answer?  Hair loss and skin issues are not something to be diagnosed by asking a breeder what they think.  This is an issue that needs to be adressed by your vet.  If what the vet is doing so far is just adressing outside causes then you need to start looking at genetic causes.  A skin biopsy needs to be done.  I do not claim to be a vet.  I am a breeder of POODLES.  If you are not willing to take someones suggestions and are going to get pissy about it then dont ask.