Help!Dog Dying 3 months of diarrhea

[eli]

I need help! My dog has lost 20 pounds in 3 months. She was diagnosed with irritable bowel syndrome and was prescribed prednasone. Now that drug has pushed her into a diabetic state so she has begun insulin shots. The internal medicine specialist said all his treatments are not working on her and she is falling into the mystery illness category. She has always been a healthy big dog and now cannot stop having diarrhea. She is only 2!! We have tried prescription foods, medications, natural foods and she continues to lose weight because she's not absorbing anything. The Veterinarian said if she does not put the weight back on we will need to consider other options...
Can anyone please point me in another direction and get my dog well???