My Bichon won't stop itching!

Hi,
I have a Bichon Frise who itches all the time!
I have taken her to the Vet and he has tried everything
he can think of from Omega fish oils, no corn,no wheat
diets. Antihistamines,neo-predef powder for her feet.
All kinds of different shampoos from expensive grooms,etc...
Throughout all of this she has been on prednisone.
If she goes a day without the pred.she is so misrable.
Please help!! She's only 1 1/2 yrs old. I'm so afraid of what
the steroids are doing to her health!!
Thanks,
izzy14