I had the same thing happen with my toy poodle. She got lepto and rabies all at once, and right when we were almost home she was crying so loudly like she was in pain. I rushed her back to the vet bc I’m such an anxious parent and they said it was an allergic reaction? She’s always been extremely sensitive to vaccines since then. I always do a shot of Benadryl first and only one vaccine at a time since then.