What could be wrong with my dog?

I'm not a vet, but just a suggestion. Try touching the dog in different places and watch her reaction. If she moves away from the touch, whines, or looks like she is in pain....then that might be the place where she is hurt. Not sure if the larger dog is aggressive while playing, but might have pounced on your medium size dog and possibly could have hurt her internally.

If she is not eating, trouble breathing and swallowing, and reluctant to walk; it sounds like something is definately going on and I would trust a vet to find out the problem.

Please though make sure she is definately drinking water. Keep her hydrated.

Lastly, if you can....open her mouth and just check/look around in there. Maybe there is something stuck (like those weeds that stick to your socks and to the fur on a dog). Just a thought.

Good luck.

It could be anything from a tick to a punctured lung but either way she should be rushed to the vets now.

If this was my dog right now i'd be halfway to the emergency vet and wouldn't even wait long enough to change out of my PJ's!

How on earth do you expect anyone to diagnose your dog without examining it? Just upload your dog as an attachment (.dog file) and we'll all have a good look.

Swallowing a foreign object could cause problems.

Cancer maybe :( take your dog to a vet ASAP!