skin problem on my german shepherd

Question
I have an 11 month old male shepherd. A couple of months ago I noticed he was scratching and chewing on his flanks and on the edges of his hips and belly.  He ended up with a staph infection and my vet put him on antibiotics.  I also changed his food from Iams to Purina One Lamb and Rice (which I had fed my previous shepherd and had very good luck)  He seemed to be doing much better for a while.  However, I have noticed that he is chewing again and has reddish black splotches over his abdomen, flanks, and front of his hips.  His is flaky around his hairline on his abdomen.  Can you tell me what may be causing this?
Thanks

Answer
It could still be a skin infection.  There are other things besides foods that cause pyoderma.  I would ask the vet for more antibiotics and I would have the dog treated for external parasites such as sarcoptic mange, even if your vet doesn't diagnose them on skin scrapings.