My dog has been having severe allergic reactions, can anyone help.?

I have went to 4 different vets in 2 weeks, and so far no one can explain why my dog has almost lost her life to a severe allergic reaction that almost closed her breathing pages. My dog has had blood in her urine, and her tummy is red and hot. I have done everything humanly possible and avoided any trigger for allergies, my floor and anything in her reach is spotless & chemical/dye free. She is on antibiotics but she is still ping blood, her blood test have came up normal . My mom thinks it was the tainted dog food, but is on a mild home-made diet from the vet but only a little better, also her kidneys tested normal. Her hemoglobin (red blood cells) were up. She cleared up with prednisone but they won't leave her on it, and I'm afriad she'll go into another attack. Please remember before leaving comments, I have taken her to many vets. Thank you all.