i have 3 dogs who are unrelated (an 8 month old havanese, a 3 year old havanese-bichon mix and a 12 year old yorkshire terrier). they all have been sick with chronic diarrhea for the past 4 months. no one can seem to diagnose them. all tests and cultures come back negative. they've been on 3 different medications, none of which have cured them. flagel and tylan both suppressed the disease while they were on the medicine, but once they stopped they all got sick again 3 days later. most recently, we've tried panacur c, and that did not work at all. what could be wrong with them? are there any other medication options? i don't want to have to keep them on tylan the rest of their lives (which is what one vet is suggesting), i want a cure and no one can seem to offer that! help!