Diarrhea Diarrhea too long!!!!

Miss Piggy started having poops with points at one end about 3-4 weeks ago. Then occasionally a soft lump of pop, and back to solid. We went on vacation (of course) at the time it became soft-runny and took her to the vet. No bacteria or parasites were found in fecal test. The vet had her go on probiotic powder mixed with apple sauce which took care of it after 4-5 days. We came home and it became runny again within a few days. She was eating and acting great during this whole time so we were extremely alarmed. At the second visit she had all but stopped eating and poops are liquid/mush and we are now doing critical care, Medicam, probiotic, and gas drops. We have even gone as far as tiny amounts of diarrhea liquid for cats. She maintains her weight and hydration still, not 100% perky but plenty enough to fight feedings! Vet suggested to do this for a week (!) then try antibiotic even though fecal test was normal earlier on. She will still devour banana and dried apple. Anything not fiber of course.
Anyone go through this before?
She is about 3 years old and has always been healthy, crazy about Timothy hay and pellets. Loves her tiny tomatoes!