Rash on lower abdomen only

Question
She gets a red rash on her lower abdomen about every 2-3 months and I have to take her in for a steroid shot and antibiotics.  The Vet and I are at a loss because we have kept her on Lamb and Rice dry food for almost a year.  He is not inclined to believe it is food related but feels keeping her on this is one less thing to consider.  It is right where she sits down to pee. the area on her tummy with no hair.  She is healthy and active otherwise....do you have any thoughts on this.  P.S. I know we can sent her to a specialist but you are talking major expenses to run allergy test.

Answer
How old is she?  I have seen puppies with something similar, and my vet said it was the immune system not kicking in yet.  I would think it would have by over a year old.  Keep working with the vet.  He is right about not jumping around various foods.