dog is curiously ill

[Cheryl]

I have a 3yr old dog, Tucker - most closely resembles English Shepherd - who is sick. Usually he's very cheerful and wiggly/waggly. Yesterday he whimpered (!) and moved sluggishly upon greeting me. I gave him a thorough visual and tactile exam but could not discover any areas of injury. His nose is cold and slightly damp, his paws feel good, his ear temp is normal and eyes are clear. He ate and drank and did his business properly outside - seemed to have slight trouble with bowel movement. His breathing seems to be irregular - shallow.

Any idea what the trouble might be?