My Friends Dog Has Been Vomiting Everyday For A Couple

My friends dog has been vomiting everyday for a couple of months. Her vet did stomach surgery about three weeks ago and said he couldn't find any thing and put the dog on stomach pills. She has always eaten dog food and not been sick before. Sometimes she has diareha and has started panting a lot. Zoey, the dog is 11 or twelve, she was a rescue dog so we don't know any background on her. The vet has tried different kinds of dogfood, wet, she always had dry before but now she doesn't like anything, not even scrambled eggs. Any sugestions? Thanks Phyllis