Very itchy dog.

My sweet Molly has a skin infection my recent visit to the vet diagnosed it as ringworm and put her on 100 milligrams ketaconazole po daily for 14 days, she is 10 lbs. She has been taking it for 5 days and there is no improvement. The main lesion is on her back and is now spreading and with yellow crusting. She has a foul odor sort of like urine but not quite. She is 7 hrs old and we dealwith this same type of rash at least 7 months of each year. We go in a cycle of the first diagnosis is allergy, then they say fleas or fungal then she gets a secondary infection and we always end up on clindamycin. I have tried every type of food out there including purely synthetic hypoallergenic food at $60 a bag, I have cleaned, cleaned and clean some more. Thrown away bedding over and over again and nothing really seems to help. This poor baby dog scratches herself insane she looks herself until yeast develops between her paws and in her ears then we have to go to special air solutions that have trizul/synoptic/diflucan/Bayer which work great but the vet charges $82 a bottle for and won't write a script for BC he says it is his own mixture. I am a nurse practitioner so I understand the cycle of treatment and effects of medication side effects. I just want her to feel better....is there anything that you can recommend? I am truly begging! Lol. I look forward to hearing from you.
Cheryll and Molly