I've recently taken my three females to the vet and had them spayed. When they came home the first night things seemed normal. I gave them all their Onsoir pain medicine that the vet provided. The day after I noticed that one of them had not been eating which is very unusual for her. The manual for the Onsoir tablets said that not eating could be a sign that they are having a reaction to the medicine so I stopped giving her the pain medicine, but continued giving it to the others. The next day the same cat has started vomiting. Again, I still think it is a reaction to the medicine so I wait for it to pass out of her system. It has been four days and not only is she still vomiting, but ALL the girls are vomiting. I would still consider the pain medicine as the cause but even the male in my house who did NOT go to the vet is vomiting. I am extremely worried. I have found puddles of vomit with what looks to be blood in it. I haven't changed their food, could it be viral? What could it be?