Pet Emergency Care

[getwell]

Hi
I have a female Papillon, late Saturday night she started vomiting and a bit later very loose stools. This went on all night. She seemed so much better the Sunday morning I thought it was all over with, however late Sunday night as she was getting up to move she screamed out in pain. She now seems very stiff in her hindquarters and relucant to move. No more vomiting still very loose stools this am and stiff in hindquarters. My other dog (female Pom) is fine. What could this be?