First - what a great foster mom you are! Taking care of your own and your fosters. Blessings to you for opening your heart and your home in this way.
I hope by now the panicky feeling is over - if not sit down with a cup of tea and cuddle Andy until you both feel better.
The vet and the foster lady should have valued your experience more and reacted differently. They didn't and you can't change that so ... water under the bridge.
Hope the day got better from there.