pug with itching problem

Question
Hello ~ I have a 1 year old pug.  We have only had him for about 2 months.  When we first got Piggy, he was fine.  After a couple of weeks he began itching his hind end.  I took him to a vet and they thought it was allergies.  Give him benadryl and he should be better.  The scratching continued.  Piggy itches near his tail and now has small sores that have crusted over.  He does not itch his paws or face area.  He sits and spins circles trying to scratch the back of his legs and rump.  After a week of no improvements, we went to another vet.  This vet thought he may have a flee allergy.  He was given frontline, put on an antibiotic, prednisone and a medicated shampoo.  He did show some improvements.  I started to research online to find some alternative solutions.  Found Nordic Natural Omega 3 for pet could help with itchy skin.  Piggy has been on those for almost 2 weeks.  Last week the itching set in again terrible.  His skin was very pink under arm pits and across the back end. Took him back to the vet.  Again frontline, antibiotic and prednisone.  This is day 6, he is not really showing any improvements.  The itching still seems to be the rear of the dog.  He is not itching the front half very much.  I have checked his paws etc and see not signs of irritation.  Looking for some advice, it scares me to have him on prednisone very long because of the side effects.  This poor dog needs some relief.  PS I have changed his dog food 3 different times.  No change in skin condition.  Any insight you may have would be greatly appreciated.

Answer
When dogs on steroids itch that much, I have to think about some kind of parasitic problem, like sarcoptic mange.  Have you had the dog treated for any skin parasites?  HAve you seen any fleas?  he may need a higher dose of steroids if it is a flea allergy.