Skin infection on 13 year old Cocker Spaniel

Question
We have a 13 year old Cocker Spaniel.  I know they are known for ear and skin problems but the skin is becoming out of control.  He started getting sores under his chin/chest area. They are now popping up randomly over his body.  

We took him to the vet and they wanted to do a million tests to figure out what it is.  We have been going to this vet for over 2 years now and have seen this skin irritation before (not as bad) and the vet never seemed to figure out what it was.  Mites?  Yeast?  Allergy?  We did follow the vet's instructions and changed his food to a FP food, we bath him min. every 3 days with special shampoo we purchased from the vet.  We clean his ears with the solution from the vet.  We started him on antibiotics Saturday and throughout this process we have concocted our own cream of Neosporin, Lotrimin & Cortizone cream to put on the affected skin areas.  This seems to help stop the new sores from progressing and helps them heal, but new sores will appear in other areas.  Oh and did I mention the horrible smell?

We know that maybe he is not able to fight off whatever this is due to his age, but want to do what we can to make him comfortable.  We feel that to spend a ton of money on tests after 2 years of this is getting ridiculous and was hoping you might have some ideas for us to try on our own.  We're not really feeling very confident in our current Vet and also don't really have the money right now for random testing.

Hope this is enough info for some advice.

Thanks!

Answer
This may be a yeast infection, but without an exam it is hard for me to be sure. HAs your dog been on Ketoconazole or itraconazole?  There may be allergies causing all of this and if the dog has not been on high dose steroids for a month, then it may be time to try that. Continue the bathing as this helps with the smell.