My Parrot died ? Now another has same problem ! Wot do i do ?

My Af Grey died about a year ago, it went really thin even though it was well fed and got diahorria and died. I brought it 2vet 4postmortem and was told it was a gastric yeast infection but now i have two parrots which look to have same problem. Has anyone else parrots had these symptons as i dont think my vet has a clue and the other nearest is 5 hours drive away and i dont want to put my sick birds through it as id say the stress will finish them ! HHHEEELLLPPPPP