skin lesions/ dry scabs/ hair loss

Question
Hello,
My fiancee and I rescued an ~9 week old puppy, Newman, from a local shelter. They told us he is a chocolate lab/Aussie mix, but, except for a white stripe down his chest, he looks like a choc lab. About two months ago, towards the end of Summer here in Houston TX, i noticed something small rubbery white in is stool. We immediately thought tapeworm. Our vet agreed and we gave him a pill she recommended. A few days later, my fiancee decided to give him a bath with a mild flea shampoo, since Newman is always itching. About a week later, Newman developed a rash on his belly. He had several bump like mosquito bites all over exposed areas of his belly. Once again to the vet, and she told us it was a staph infection and treated him with antibiotics, which we fed him for the next 10 days, twice a day. It worked. Bumps went away. Most recently, I switched Newman from Pedigree Puppy food to Blue Buffalo puppy food, which he seems to enjoy.
Last week I noticed a lesion on the middle of his back, which seemed to be secreting a sticky fluid. I applied Neosporin. the next day legion seemed to be drying out but it was covering a slightly larger area, and a new one was starting to show up a bit lower down his back. In addition, the hair around the affected area was falling in clumps. at the vet again, she scrapped a sample which she checked for mange... Negative. Shes currently running a test for ringworm, which has not yet developed. she gave us a shampoo, Etiderm, and told us to bathe him twice/wk with it. she also recommended fish oil in his food....
Newman is showing no noticeable signs of sickness, but he itches alot and now has two bald spots on his back showing scabs.. It very worried for him. is there something else we should be aware of or should do? any other thoughts on what it could be? is our vet taking the correct steps? things seem to getting worse quickly.
we also have a 2 yr old chihuahua/pom mix in perfect health with not skin issues.
thank you for your time. I'll be happy to forward pics if necessary.
Regards,
Ric J.

Answer
Some pups have allergies to things in their foods.  You might need to use a very strict hypoallergenic diet. In addition, these bacterial infections will continue as a result of the food allergy, so keep up the shampoos and the antibiotics. Most pups outgrow these allergies by a year of age.  I would also advise treating the pup for mange even thought the skin scrapings are negative.