Sounds like an allergy. Normally dogs don't get a rash what it is, is a bacterial infection of the skin. I work at a vet derm specialist and there are many causes for an allergy. First get any secondary infection cleared with some antibiotics. Second the key to managing allergies could be diet or environmental or flea. Definitely have your vet take another look. You can go to acvd (dot) org and look for a vet derm in your area if your are in the states. If there isn't one nearby ask you vet to call and at least consult with one on the phone. The derm I work for does it all the time and it a good way to get your vet some expert advice for free. You mention the ears are they infected too? Smell? Crusty on the edges? Ear and skin infections are all secondary causes of allergies. Like I said management is key. There are many other antihistamines out there and sometimes like humans one will work for a while and then you may need to change. You can read some of my earlier posts about food allergies and elimination diets too that can help. Remember that to keep costs down for meds try having your vet call the local walmart pharmacy if you need an antibiotic like cephalexin they offer $4 generics. Also online pharmacy like costco (no membership needed for Rx's) they offer free shipping and have cheap scripts. Long term steroid use can be harmful so I would look for the root of the allergy and try to manage it without the steroid. If cost isn't an issue allergy testing and shots are the best route or if shots are not an option ask about atopica (cyclosporin is the human version usually cheaper). Your vet should be willing to work with you on the drug issue and saving $ if not find a new vet. Keep in mind about a derm consult. Reg vets only get a 2 week rotation in school on dermatology so it really is worth seeing a specialist to get the correct treatment and not waste money on things that reg vets don't realize won't work. If you click on my name you can post me a note anytime with other questions. Good luck!
I don't think she is losing any hair. When she had the first skin problem they shaved her underside and it is starting to grow back in now.
Is she losing her hair? She might be allergic to something, even benadryl. Could she have picked up fleas somewhere? Some dogs are allergic to fleas.
Maybe you should take her back to the vet.
lonewolf