Hello, I'm a small animal veterinarian and I can help answer your question about Archie.
These symptoms have just been going on today?
Did he overdue it playing with another dog, going on a long hike?
Is there any potential for an injury?
Almost sounds like a rib injury if he's painful when breathing and when getting up from being on his side.
They can also become sore in the intercostal (between the rib) muscles from playing too rough
Is his breathing fairly normal?
Any other symptoms? Is he eating/drinking normally? Urination/defecation normal?
That is strange. Again, sounds like pain in the rib area because it's only bothering him with the bark and when he lays on it.
It's possible that this will pass once the soreness subsides.
If he develops any other soreness, or any other symptoms, I would have him seen by his regular vet.
If you want to give him some aspirin to help with the pain, I can calculate a dose if you give me an approx weight
Okay, so the baby aspirin (81mg) will be fine for him. Make sure he isn't getting any other anti-inflammatory medications or steroids from another vet while taking this drug.